Question 1068570
{{{x^2+17x+72=(x+9)(x+8)}}}, so the two pool dimensions are  {{{x+9}}} and {{{x+8}}}.


The walkway around the pool makes the entire outer dimensions (outer border)  {{{x+9+2*3=highlight(x+15)}}}  and  {{{x+8+2*3=highlight(x+14)}}}.