①2/5+1/5x=1
2+x=5
x=5-2
x=3
②x-1/3x=2.6
2x/3=2.6
x/3=1.3
x=3.9
③15%x-8=7
0.15x=7+8
0.15x=15
x=100
④1/3x+1/5=1
5x+3=15
5x=15-3
5x=12
x=12/5