Partial products is breaking down every number in multiplication and adding them. Regrouping is grouping number them adding them. They are different because one is taking all the numbers broken down, while the other is just a couple of the number.
It's asking you to find the derivative, which is -0.06x+1.8, and then, when it equals zero, it has reached the top. that is, -0.06x+1.8=0, or x= 30. plug that into the original formula, and you get -0.03(30)²+1.8(30)-24, or 3. the answer is 3 (inches, presumably)
