8(3-5х)=7(8+3х)
8*3-8*5х=7*8+7*3х
24-40х=56+21х
24-56=21х+40х
-32=61х
х=-32/61
Проверка:
8(3-5*(-32/61))=8*(3-5*(-32)/61)=8*(3+160/61)=8*(61*3/61+160/61)=
=8*(183/61+160/61)=8*343/61=2744/61
7*(8+3*(-32/61)=7*(8+3*(-32)/61)=7*(8-96/61)=7*(61*8/61-96/61)=
=7*(488/61-96/61)=7*392/61=2744/61
Ответ: -32/61