a)To find the y intercepts you need to factor it out to find the zeros. You're answer isn't quite right. (look at the power of your 3)
b)When you have a function of x f(x) think of it as your y value. So you can think of your coordinates as so your y value will be the answer when you plug 3.5 into the formula.
if you want to find the x-intercepts.. the point were x=0 just plug it in and go:
c) to find your highest point you can imagine the two (x values) at the y intercepts. Because one is going up and the other is going down, so the point between will be the highest. Plug it into your f(x) equation and see how high it will go. Hint: look at your answer to a) and my example numbers in b).