Explanation:

a = 52^o [vertical opp. ∠s are equal]
a = b = 52^o [Alternate ∠s]
b = c = 52^o [vertical opp ∠s]
c + x + 35^o = 180^o [sum of angles in a triangle]
52^o + x + 35^o = 180^o
x + 87^o = 180^o
x = 180^o - 87^o = 93^o