Question

how to get the answer for 7x-3y+8x

Answer 1

what you have is an expression

expressions do not have an answer, they can only be simplified

assuming your question is, how do i simplify the expression "7x-3y+8x"

this can be done by adding like terms

an example of this
say the question is simplify x+2y+3z-x+2y

then we can only add the x to the -x to each other
and we can only add the 2y to the 2y
so the simplified expression of the example would be
4y+3z

Answer 2

it is an expression...?