Question

4 = x + 8 qual valor?

Answer 1

4 = x + 8 => 
x + 8 = 4 =>
x = 4 - 8
x = -4

Entendeu?
Bons estudos!

Answer 2

Boa tarde

x + 8 = 4 

x + 8 - 8 = 4 - 8

x = -4