7分之3-9分之4+2÷7
=3/7+2/7-4/9
=5/7-4/9
=17/63
7分之2X=12
2X=84
X=42
6分之X-4=10分之X+2
5(X-4)=3(X+2)
5X-20=3X+6
2X=26
X=13
12分之X+15分之X=36
5X+4X=2160
9X=2160
X=240