(0.3+x)*2=8
0.3+x=8÷2
0.3+x=4
x=4-0.3
x=3.7
7+5x=42
5x=42-7
5x=35
x=35÷5
x=7
1.3x-x=18.6
0.3x=18.6
x=18.6÷0.3
x=62