Okay. So the problem is asking you to substitute various expressions for f(x) into the formula
So all you do is take the expression and plug it in where f(x) is. For example, for the first one the expression is 3x-7. So we want to first replace any f(x) we find with 3x-7:
Second, we see that f(x+h) is also a function, even though it doesn't look exactly like f(x). What we have to do to figure out f(x+h) is do the exact same thing we did with the regular f(x) - we substituted 3x-7 - except instead of just plain x, we do it with x+h. So:
Now, since we've figured out f(x+h), we can substitute the value we got back into the original equation. Now we have:
When we multiply this out and simplify algebraically, we get
What this is is really a beginning calculus problem; it's the formula for finding a derivative using limits. So you might get better answers trying the calculus board. Can you solve the second one on your own? If not, and if I didn't explain in enough detail, just ask and I'll try to help you out some more.