Simplify:
9 - [10 - {20 - (15 - 9-3¯)}].
Explanation:
= 9 - [10 - {20 - (15 - 6)}]
= 9 - [10 - {20 - 9}]
= 9 - [10 - 11]
= 9 - [-1]
= 10
Hence, option (a).