(∠BOD, z); (∠DOF, y ) are pair of vertically opposite angles.
So, ∠BOD = z = 90°
∠DOF = y = 50°
[Vertically opposite angles are equal.]
Now, x + y + z = 180° [Linear pair] [AB is a straight line]
x + y + z = 180°
x + 50° + 90° = 180°
x = 180° – 140°
x = 40°
Hence values of x, y, z and u are 40°, 50°, 90° and 40° respectively.