Question

What is y when -21=3(y-5)-6y

Answer 1

-21 = 3y - 15 - 6y. Then do like terms:
-21 = -3y - 15
+15 +15
-6 = -3y
-3 -3
y = 2
Hope this helps :)

Answer 2

-21 = 3(y - 5) - 6y

Distribute 3:
-21 = 3y - 15 - 6y

Combine like terms:
-21 = -3y - 15

Isolate ys to the left hand side:
3y = 21 - 15

Combine like terms:
3y = 6

Divide both sides by 3:
y = 2

Answer: y = 2