The triangle PQR above is

Explanation

∠PQR = 180 - 128 (∠s on a straight line)
= 52^o
∠QPR + 76 + 52 = 180(extr ∠ = sum of intr. opp ∠s)
∠QPR + 128 = 180
∠QPR = 180 - 128
= 52^o
∴ΔPQR is an isosceles triangle