In the following figures, find the lettered angles.

(i) Let a be represented by ∠1 and ∠2

    ∠a = ∠1 + ∠2

    ∠1 = 35° (Alternate interior angles)

    ∠2 = 55° (Alternate interior angles)

    ∠1 + ∠2 = 35° + 55°

    ∠a = 90°

     Thus, ∠a = 90°