## Algebra 1: Common Core (15th Edition)

a) 13.5 b) if $a=b$
a) The opposite of $-8.7$ is $+8.7$, so you add 4.8 and 8.7 to get the answer. b) if $a=b$, then $a-b=0$, and $b-a=0$. Therefore, $a-b=b-a$