Answer:
∆ PQR is congruent to ∆ STU
This means --
P = S
Q = T
R = U
R = 80°
S = P = 70°
So in ∆PQR, we know R = 80° , P = 70° and Q = ?
Using angle sum property of triangle,
P+ Q + R = 180°
70° + 80° + Q = 180°
150° + Q = 180°
Q = 30°
Hope This Helps :D
