3+2*(x:4-12)=9
2*(x:4-12)=6
x:4-12=3
x:4=15
x=15/4
3+2*(x:4-12) = 9
2*(x:4-12) = 9-3 = 6
x:4-12 = 6:2 = 3
x:4 = 12+3 = 15
x = 15:4 = 3,75