In part 4, you've found that a minimum occurs at and a maximum occurs at (I didn't check if this was correct). This is where the min/max point is, and should be the only answer for part 4. The min/max value is the second number you wrote down in each case: is a minimum value and is your maximum value. These second numbers are the answers to part 5.
Putting the two into pairs as you did in part 4 actually gives you the answer for part 6. So in essence, you implicitly answered parts 5 and 6 in your answer to part 4.