I would first rearrange the second equation to get x by itself
x+15=3y
x=3y-15
Then I would substitute 3y-15 in for x in the first equation. I would do this because x has the same value as 3y-15
4(3y-15)+20=5y
12y-60+20=5y
12y-40=5y
-40=-7y
5.7=y
Then plug y back into an equation to get x
x+15=3(5.7)
x+15=17.1
x=2.1
Hope this is correct :)
