0.4x-0.4乘10.8=20
0.4（x-10.8）=20
x-10.8=20/0.4
x-10.8=50
x=50+10.8
x=60.8
6分之5：x=9分之5:5分之2
5/9 x=5/6 X 2/5
5/9 x=1/3
x=1/3 X 9/5
x=3/5