Pre-cal question (parabolic arch)

Question

hey, I'm having a hard time solving part (b) I got the answer for part (a)

An arch has the shape of the parabola y = 10 - x^2. A rectangle is fit under the arch by selecting a point (x, y) on the parabola (see the figure).

(a) Express the area A of the rectangle in terms of x. (A: 20x-2x^3)

(b) If x = 1, the rectangle has base 2 and height 3. Find the

base of a second rectangle that has the same area.

thank you.

Answer 1

(b) At x = 1 the base is 2 and the height is 10 - 1², or 9.