To make a puzzle, Denzel draws lines a and b to cut along on a
square piece of posterboard. He wants to draw line c so that it is
parallel to line b.
What should the
measure of 21 be?
Explain.

answer: (c) m∠qpo + (2x + 16)° = 180°

step-by-step explanation:

the opposite angles of a quadrilateral are supplementary.

so, ∠o + ∠q = 180°   and   ∠p + ∠r = 180°

since ∠r = 2x + 16°, we can use substitution as follows:

∠p + ∠r = 180°

∠p + (2x + 16)° = 180°