The interior angles in a 4 sided polygon add up to 360°. You are already given two measurements of 90°, so you know that the lastvtwo angles sum to 360-90-90= 180°.
Put this information into an equation and solve for x:
(7x+27)°+(9x-7)°=180°
7x+27°+9x-7°=180°
16x+20°=180°
16x=160°
x=10°
Angle B is (7x+27)°, so just substitute x:
B = 7(10)+27
B = 70+27
B = 97°