Question

Write an equivalent expression for 5x + 2y + 3x

Answer 1

Well, if you combine like terms that version of this equation would be equivalent. 
5x + 2y + 3x = 8x + 2y

I'm not sure if this is the answer you're looking for but, I hope this helps!

Answer 2

An equivalent expression for this equation can be formed by simplifying. You can and the like terms of x's.
Doing this, you get 8x+2y.
Hope this helps