Answer :

-2 i think all you have to do is 5x divided each side 5x divide by 10=- 2
Because they both equal 'y' you can make them equal to each other.
5x-10=3x+8
-Add 10 on both sides-
5x=3x+8+10
-Minus 3x on both sides-
5x-3x=18
2x=18
-Divide by 2-
x=9