Question

-2 = g - 9 solve equation

Answer 1

OK.  Hold on tight.  Here we go.
Remember ... the "solution" is the number that 'g' must be
in order to make the equation a true statement.

The original equation:   You said that  -2 = g - 9

Now, let's add  9  to each side:             7 = g .

Answer 2

-2=g-9
-2+9=g
g=7

Proof of answer if it's required on your test

-2= (7)-9
-2= 7-9
-2= -2