Question

-9 + m = 20

Explanation:

Step1: Isolate the variable m.

Add 9 to both sides of the equation: $-9 + m+9=20 + 9$.

Step2: Simplify both sides.

On the left - hand side, $-9 + 9=0$, so $m=20 + 9$.

Answer:

$m = 29$