Question 943701
u, the uniform width
w, the width of the pool
L, the length of the pool
b, the area of the walkway, think "border"
-
w=6
L=6
b=189
find u, or solve for u.


Pool area, {{{wL}}};
Pool Plus walkway/border area, {{{(w+2u)(L+2u)}}};
Walkway area, {{{(w+2u)(L+2u)-wL=b}}};


The description gives w=L, so the last equation can be adjusted according to that simple substitution, the pool being square-shaped:
{{{(w+2u)(w+2u)-w^2=b}}}
and then starting to simplify
{{{w^2+4wu+4u^2-w^2=b}}}
{{{4wu+4u^2=b}}}
{{{highlight(4u^2+4wu-b=0)}}} and you should know what to do from here...  remember, the UNKNOWN variable is u.