Answer
$ a.\quad$the additive inverse of $-7$ is $7$
$b.\quad 5-(-7)=5+7$
Work Step by Step
a. the additive inverse of $-7$ is $7$
b.
To subtract $b$ from $a,\ \mathrm{a}\mathrm{d}\mathrm{d}$ the opposite, or additive inverse, of $b$ to $a.$
$a-b=a+(-b)$
$5-(-7)=5+7$
$=12$
