7.6+3x=12.1
3x=12.1-7.6
x=4.5÷3
x=1.5
4×2.5-9x=1
10-9x=1
9x=10-1
x=9÷9
x=1
3.5x+1.5x=7.5
(3.5+1.5)x=7.5
5x=7.5
x=1.5