×+4/5+(-0,2)=y/2+1/4 ×0,125
×+4/5-0,2=y/2+1/4×1/8
×+4/5-1/5=y/2+1/32
×+3/5=y/2+1/32
×-y/2=1/32-3/5
×-y/2=-91/160
160×-80y=-91