Question 914207
Corner to corner, the entire pool and deck, and using x for the uniform width of the deck,
Total Area is {{{(20+2x)(28+2x)=884}}} square feet.


Just the area for the pool is {{{20*28}}} square feet.


The area for just the deck is then {{{884-20*28=324}}} square feet;
{{{highlight_green((20+2x)(28+2x)-20*28=324)}}}, the difference between the areas of deck & pool and the pool
is the area of just the deck.


STEPS
{{{20*28+56x+40x+4x^2-20*28=324}}}
{{{4x^2+96x=324}}}
{{{4x^2+96x-324=0}}}
{{{x^2+24x-81=0}}}
{{{(x-3)(x+27)=0}}}


The meaningful answer is {{{highlight(x=3)}}} feet.