4x(x-20)^2 Use a graphing calculator to approximate the values of x that produce a volume of 4500

Question

Note: There are 3 values of x that produce the given value but only two of them are acceptable in the context of the problem. List the two answers, to at least one decimal place, separated by commas.

Answer 1

My graphing calculator gives the three roots as:

 

5, (-5/2)(√3 - 7), (5/2)(7 + √3)

 

I do not know which two are acceptable.