3x/7+x/3=3/21
9x/21+7x/21=3/21
16x/21=3/21
16x=3
x=3/16
(2) 2x-3x/5=1
7x/5=1
x=5/7
(3) x-x/6=5/12
5x/6=5/12
10x/12=5/12
10x=5
x=1/2