问题补充：六年级数学题解方程：
①1/4x-4x=1/2
-15/4x=1/2
x=-2/15
②50%x-5/6=5/12
0.5x=5/12+5/6
0.5x=5/4
x=5/2
③6x+4(20-x)=90
6x+80-4x=90
2x=90-80
x=5