You want to combine like terms so that means each term has to have the same variable and exponent. There are no exponents so now we look at the variable. So, +8x and -x have the same variable so add them together. 8x+ -x which is the same as subtracting since -x is negative.
8x-x= 7x 7x is positive
You still have 3 and - 2y +4y and +1. Now combine -2y and +4y
-2y + 4y = 2y
you still have 2 like terms, 3 and 1.
3+ 1 is 4
so its 4+2y+7x