Question 85763
Okay,

We are given the polynomial of 15n+6n^2-3n^2+4n+8+7

When we add like terms, that means we add numbers that have the same ending to them. For instance 2n and 3n are like terms because they both have an n attached to them. 2x^2 and 5x^2 are like terms because they both have x^2 attached to them. However, 2x and 3y would not be like terms, because they do not have the same thing attached to them. Similarly, 5x^2 and 6x^3 would not be like terms because even though they have x attached to them, they don't have the same power. When we add like terms, we take all those terms that have the same endings and add them together.

Now lets look at your problem 15n+6n^2-3n^2+4n+8+7.
First, lets take the 15n, it has an n attached to it. There is also an n attached to a 4, so we add those together. Now we rewrite the problem with those two terms combined.

19n+6n^2-3n^2+8+7 ( notice how I took out the 4n, because it is now added with the 15n to make 19n)

ok, now we look to the next term, 6n^2, is there another number that has n^2 attached to it? Yes there is 3n^2, however if you look at the problem, we have to subtract. So we now have to subtract 3n^2 from 6n^2 and rewrite the problem

19n+3n^2+8+7

Now lets look at the next number 8. It has nothing attached to it, so any other number that doesn't have anything attached to it is a like term. 7 has nothing attached so its a like term and the problem says we have to add them. So lets add 7+8 and rewrite the problem with our new changes.

19n+3n^2+15

We now have no more terms and have come to the end of the problem and thus we are finished. The answer is: 19n+3n^2=15

Hope this helped!