1. Complementary angles are any 2 angles whose sum is 90°
 Complementary angles are any 2 angles whose sum is 180°
a) BXC and CXD add up to 90°, so they are 2 complementary angles
b) AXC and CXD add up to 180°, so they are 2 supplementary angles
c) 2x+40°=90° (as BXC and CXD are complementary)
 2x=90°- 40°
 2x=50°
 x=50°/2=25° 
 5y=90° 

 y=18°