4*(x-0.5)=4/5
x-0.5=4/5÷4
x-0.5=0.2
x=0.7
1/4*（x-0.75)=13/16
x-0.75=13/16÷1/4
x-0.75=13/4
x=13/4+3/4
x=4
20％x=3/5-x
(1+20%)x=3/5
1.2x=0.6
x=1/2