5x+15-6+7x
15-6= 9.
5=7= 12
12x+9 .
Answer:
see below
Step-by-step explanation:
Addition and subtraction are both closed under polynomials.
That means that when we add and subtract polynomials, we will end up with a polynomial
f(x) + g(x) will = always be a polynomial when we start with polynomials
f(x) - g(x) will = always be a polynomial when we start with polynomials