Respuesta :

Subtract 9 from both sides

b = -12 - 9

simplify -12 - 9 

Answer: b = -21

9 + -21 = -12 is true.

simplify brackets

simplify q + -9 to q - 9

add 9 to both sides

simplify 12 + 9 to 21

q = 21

21 + -9 = 12 is true.