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Explanation:

Using the information given in the questions let us tabulate the rates of the seats in the different rows.

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Following condition (4) as Jayanta, Ajit and Byomkesh sit on seats marked by the same letter in increasing order of row in numbers and paid different amounts, the only way this would be possible is if they sat in rows 10, 11 and 12 respectively, either on the window seat or the aisle seat. So this would lead to 2 possible cases.
Case 1: Jayanta, Ajit and Byomkesh sit on the window seat in consecutive rows. In this case, as Manik sits adjacent to Jayanta, it would imply Manik sits on the middle seat next to Jayanta in row 10. This further implies that Manik did not pay any additional amount for his seat. Now Jayanta, Ajit and Byomkesh would pay an amount of 300 + 200 + 1000 = Rs. 1500. So the balance amount of 4600 – 1500 = 3100 must have been paid by Gargi, Kikira, Pradosh and Tapesh and all of them have to be occupying aisle seats. However, no contribution of amounts changeable for aisle seats adds upto 3100. So case is ruled out.
Case 2. Jayanta, Ajit and Byomkesh sit on the aisle seat in rows 10, 11 and 12 respectively. Here Manik can occupy either the middle seat next to Jayanta or the aisle seat next to Jayanta. Let us assume that Manik occupies the middle seat in row 10 next to Jayanta. In that case, cost of 3 aisle seats adds upto 4600 – (1000 + 500 + 400) = 2900. However, no contribution of amounts chargeable for the above mentioned seats adds upto 2900. So then Manik can only sit on the aisle seat adjacent to Jayanta in row 10. The total amount of seats chargeable to Jayanta, Ajit, Byomkesh and Manik adds upto 1000 + 500 + 400 + 500 = 2400. Now the balance amount of 4600 – 2400
= 2200 has to be accounted for by 4 people i.e., Gagi, Kikira, Pradosh and Tapesh. 3 of them sit on 3 window seats and one on the middle seat. Now out of Gargi and Kikira, one of them will sit on the middle seat and other on the window seat as they sit adjacent to each other. Which means that both Pradosh and Tapesh sit on the window seat. Since the amounts chargeable for the window/middle seats can only the amongst 1000, 300, 200 or 0 and the total we need to account for is 2200, at least one of the seats has to be a 1000 Rs. Seat. If we assume one of seats is Rs. 1000, then the balance amount of Rs 1200, cannot be accounted for. So there have to be at least 2 seats of Rs. 1000 each. Which means 2 out of Gargi, Kikira, Pradosh and Tapesh have to sit in the 13th row. Now these 2 people will have to be Gargi and Kikirsa as per condition (5). So each of Gargi and Kikira pay Rs. 1000 for their seat and these 2 seats will be a window and middle seat (both adjacent to each other)in the 13th row. The balance amount of Rs. 200 will be paid by Pradosh who sits on the window seat of the 20th row. This also implies that Tapesh will sit just behind Pradosh in the window seat of the 21st row. Let us represent all this information in the table given below

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J – Jayanta, M – Manik, A – Ajit, B – Byomkesh, G – Gargi, K – Kikira, P – Pradosh, T – Tapesh

Using this data let us answer the question.

As can be seen from the table, Manik was sitting in row 10.

Hence, option (a).