解方程 3/4x=5/6 1/5+4x=4/5 x-2/3x=2/9

3/4x=5/6
x=5/6*4/3
x=10/9
1/5+4x=4/5
4x=3/5
x=3/20
x-2/3x=2/9
1/3x=2/9
x=2/3
36/25×75
=36*3
=108
11/8×20/19
=11/2*5/19
=55/38
6/7×21
=6*3
=18
16/5×3÷4/5
=16/5*3*5/4
=4*3
=12
25/9÷5/4÷4/5
=25/9*4/5*5/4
=25/9
（7/8+13/16）÷13/16
=(14/16+13/16)*16/13
=14/16*16/13+13/16*16/13
=2又1/13
3/4×3/1÷19/20
=9/4*20/19
=45/19
2/5×4+2/5
=(4+1)*2/5
=2
（21/8-4/1+3/8）×4/3
=21/8*4/3-4*4/3+3/8*4/3
=7/2-16/3+1/2
=4-5又1/3
=-1又1/3
（4/5×1/9）×45
=4/45*45
=4
89×87/88
=(88+1)*87/88
=87+87/88
=87又87/88
5/7×5/12+5/7×7/12
=5/7(5/12+7/12)
=5/7