Question

7-(3,1-0,1y) = -0.2y 

Answer 1

7-3.1+0.1у=-0.2у
-0.3у=3.9  (/ 0.3)
-у=13
у=-13

Answer 2

7-(3,1-0,1y) = -0.2y 
7-3.1+0.1y=-0.2y
3.9=-0.2y-0.1y
3.9=-0.3y
0.3y=-3.9
y=(-3.9)/0.3
y=(-13)
Проверка:
7-(3.1-0.1*(-13))=(-0.2)*(-13)
7-(3.1-(-1.3))=2.6
7-(3.1+1.3)=2.6
7-4.4=2.6
   2.6=2.6
Ответ: -13