1) х - 3y / y = 12
<span>x - 3y = 12y </span>
<span>x = 15y </span>
<span>2) x / y = 15y / y = 15 </span>
<span>Ответ 15 </span>
<span>3) ( 5х - 3y ) / 2x = ( 5•15y - 3y ) / ( 2•15y ) = 72y / 30y = 72/30 = 2,4 </span>
<span>Ответ 2,4</span>
<span>136-(х-90)÷4=56
</span><span>136-0,25х+22.5=56
-0.25х=56-158,5
</span>-0.25х=-102,5
х=-102,5:(-0,25)
х=410
проверка
136-(410-90)÷4=136-320:4=136-80=56