First, identify the like-terms in the equation.
5x, 2x, and 7x are all like-terms. Therefore, you can add them all, and your answer will be 14x.
Next, identify any other like-terms that you can combine in the expression. 3y and 4y, and because the expression asks you to add them, 3y + 4y = 7y.
And finally you can go ahead and combine the last two terms without exponents attached to them. (15 and 3)
Now you can re-write your simplified expression as 14x + 7y + 18