What does the perimeter of this figure consist of?

one semicircle and one line segment

one semicircle and two line segments

one semicircle and three line segments

two semicircles and two line segments

The property used in line A is the commutative property

This is the idea of adding can be done in any order, eg: 2+3 = 3+2 = 5

For this problem, 2x-20+x turns into 2x+x-20. Think of 2x-20 as 2x+(-20).

The property you would use after line B is the addition property of equality

This rule says that if a = b, then a+c = b+c. In words: we can add any number to both sides of any equation. In this case, we would add 20 to both sides to undo the "-20" on the left side.