the measures of a triangle equal 180. use that to find x.
now you know x, you know angle a is 40°, angle b is 60°, angle c is 80°.
because angle a is 40°, the first option doesn't work.
because angle b is 60°, the second option does work.
when you add angle a and b, you get 100°. complementary means it equals 90°, so the third option doesn't work.
when you add angle a and c, you get 120°, which is not 100.
51840000 cm 2