Question

sendo f(x) = 2x + 3 determine x de modo que f(x)= 15

Answer 1

15 = 2x + 3
15 - 3 =2x
12 = 2x
12/2 = x
x = 6

Answer 2

veja...

f(x)=2x+3

se F(x)=15

2x+3=15
2x=15-3
2x=12
x=12÷2

x=6