In the diagram QR ST PQ PR and lt PST 75o Find ... - WAEC Mathematics 2010 Question

In (\bigtriangleup) PQR,

Q = S = 75^o (Corresponding angle)

R = Q = 75^o (Base angles of an isosceles (\bigtriangleup))

But, y + 75^o = 180^o (Sum of angles in a straight line)

y = 180 - 75

y = 105^o