precalculus 1.7 a maximum value problem

Question

A Rectangular sheet of cardboard measures 19 iches by 22 inches. Square with side length x are cut from each corner to form a box 

  a. write equation for the volume of the box created  

  b.Determine the domain of the function in the context of the problem

  c. Sketch the graph of the volume function in the approriate window and state the window. Find the maximum volume of the box

  d. ( this is the question i have trouble ) what size square could be cut out so that the volume is at least 175 cubic inches ?

  e. What size square could be cut out so that the volume is at most 150 cubic inches

Answer 1

V = (19 - 2x)(22- 2x)x

for d.

175 ≤ (19 - 2x)(22- 2x)x

Solve for x