Question 7689
It seems like you went overboard (no pun intended) on your solutions to the swimming pool problem.

Your first try is your best and is actually correct, to some extent.

{{{Area = L*W}}}
Since L = 2x-1 and W = x+2, then the area is:

{{{A = (2x-1)(x+2)}}}
{{{A = 2x^2 + 3x - 2}}} This the polynomial that represents the area.

If x = 5, then:

{{{A = 2(5)^2 + 3(5) - 2}}}
{{{A = 50 + 15 - 2}}}
{{{A = 63 m^2}}}

Note that the area is 63 square meters, not meters.