Б(0,6x-0,5y)-5(0,7x-0,8y)
(0.6х-0.5у)-5(0.7х-0.8у)=0.6х-0.5у-3.5х+4у=-2.9х+3.5у
=0.6х-0.5у-3.5х+4у=-2.9х+3.5у