When doing this kind of problem, we have to find what F of X + H is. We have to find out what F of X is, and then we have to subtract and divide by H. So frequently, if students don't remember how to do this, I suggest starting with numbers. If I asked you what F of one is, could you find it? You'd put in one every time you saw your unknown, so 1 - 7 + 4 would be -2. If I asked you what F of 0 is, could you find it? 0 ^2 - 7 * 0 + 4. If I asked you for F of five, 5 ^2 - 7 * 5 + 425 - 35 negative 10 + 4 negative 6. So then I switch concepts and I say, well, what if I asked for F of A? Could you find F of A? And hopefully you see the pattern and you put in A every time you see the unknown. And if I ask for F of T, you would tell me we put in T every time we see the unknown. And then I ask F of 5B say we'd put in 5B every time we see the unknown. So then after that, oops, it was there. Then after that I would ask what is F of X + H? And hopefully after doing a bunch of examples, you'd say X + H ^2 -, 7 X plus H + 4. So then we would distribute and we'd get X ^2 + 2 XH plus H ^2 -7 X -7 H +4. So now we're going to put it all together. And to put it all together, we're going to say, let's see, F of X + H -, F of X all over H So we just found that F of X + H, that whole thing X ^2 + 2 XH plus H ^2 -, 7 X -7 H +4, that whole thing is just F of X + H Now we're subtracting F of X. Well, that was given as X ^2 -, 7 X +4 and that whole thing has got to be over H So now we can see the X ^2 and minus X ^2 is going to cancel. We get 2 XH plus H ^2, the -7 X and the minus. The negative minus the negative made it positive. So the seven X -7 X and positive 7X are going to cancel. We get -7 H and then the +4 and the -4 are going to cancel all over H So now we can see that every single term has an H in it. So if we factor out an H, we'd get two X + H - 7 all over H and then H / H is going to cancel. So our final answer is just going to be two X + H -, 7.