4:8=x:25
8x=100
x=12.5
0.5x-7/8=1.625
4x-7=13
4x=20
x=5
9x+3=8x+11
9x-8x=11-3
x=8
1/2x-7/9=x-1
1/2x-x=-1+7/9
-1/2x=-2/9
x=4/9