The answer is 66 for the total plus the bonus, the bonus equals 11 pizzas. It is because 55 x (1+20%)= 66 and 11. Meaning 55 pizzas times 1 + 20% equals 66, so it means that the bonus was 11 pizzas and the total that day is 66.
The two curves intersect at two points, (0, 0) and (8, 8):
The area of a semicircle with diameter is . The diameter of each cross-section is determined by the vertical distance between the two curves for any given value of between 0 and 8. Over this interval, and , so the volume of this solid is given by the integral