Discussion

Explanation:

Let us join A and D as shown below.

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In ∆CAD, external angle CDE = ∠ACD + ∠CAD

In ∆ADB, external angle BDE = ∠BAD + ∠DBA

Now, x = ∠CDE + ∠BDE = ∠ACD + ∠CAD + ∠BAD + ∠DBA

⇒ x = ∠ACD + ∠CAB + ∠BAD

⇒ x = 20 + 50 + 10 = 80°

Hence, option (c).

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