A rectangular prism with a volume of 400 cubic centimeters has the dimensions x + 1 centimeters, 2x centimeters, and x + 6 centimeters. The equation 2x^3 + 14x^2 +12x =400 can be used to find x. What is the length of the longest side? Use a graphing calculator and a system of equations to find the answer.

A) 4 centimeters

B)5 centimeters

C)8 centimeters

D)10 centimeters