-2y-39=5y-18

Add 2y to both sides and combine terms.
-2y+2y-39 = 5y+2y-18
-39=7y-18

Add 18 to both sides and combine terms.
-39+18 = 7y-18+18
-21 = 7y

Divide both sides by 7
-21/7 = 7y/7
-3 = y
Your other posts are done using the same process.