I need help on these two parts, my graphing calculator is not graphing the equation it just states error 14, please help its due today.

Question

An appliance manufacturer estimates that the profit y (in dollars) generated by producing x cooktops per month is given by the equation y = 10x + 0.5x² − 0.001x³ − 4000,

 where 0 ≤ x ≤ 450.

(b) How many cooktops must be produced to begin generating a profit? (Round your answer to the nearest whole number.)

(c) For what range of values of x is the company's profit greater than $15,000? (Enter your answer using interval notation. Round numerical values to the nearest whole number.)

Answer 1

Well, my calculator gives 88 for part b.

The graph is so steep that it is hard to tell about part c., but the graph has a maximum near x=343.