Question

Find the measure of an angle who's measure is 20 less than the measure of its supplement.

Answer 1

supplementary angles add up to 180°.

x = measure of such angle

x + 20 = measure of her sibling.

since "x" has 20 less than her sibling, then clearly her sibling has to have 20 more than "x".

$\bf (x)+\stackrel{sibling}{(x+20)}=180\implies 2x+20=180\implies 2x=160 \\\\\\ x=\cfrac{160}{2}\implies x=80$