Question 1104297
Dimensions are  {{{-15+5x}}} and {{{x}}}, for length and width, in that order.


Area was given as 540 square inches.
{{{x(5x-15)=540}}}
Simplify and solve.


Notice factor of 5 on each side.
{{{x*5*(x-3)=2*5*54}}}

{{{x(x-3)=2*54}}}

{{{highlight_green(x(x-3)=108)}}}
From here, you have two choices.  Check for factorizations for 108 which differ by 3; or continue algebra and solve a quadratic equation.