取分母的最小公倍数进行通分
1 x=15/36+12/36=27/36=3/4
2 x=13/26-10/26=3/26
3 x=7/8-6/8=1/8
x-5/12=1/3
12x-5=4
12x=9
x=3/4
5/13+x=1/2
x=1/2-5/13
x=13/26-10/26
x=3/26
7/8-x=3/4
x=7/8-3/4
x=7/8-6/8
x=1/8
x-5/12=1/3
x=5/12+4/12
x=9/12
x=3/4
5/13+x=1/2
x=1/2-5/13
x=13/26-10/26
x=3/26
7/8-x=3/4
x=7/8-3/4
x=7/8-6/8
x=1/8
2/一个小时工具备用熊