Question 279301
well {{{(20+2w)(40+2w)=1500}}} w=width of sidewalk
{{{(800+80w+20w+4w^2)=1500}}} 
{{{800+100w+4w^2=1500}}}
{{{-700+100w+4w^2=0}}}
{{{4(-175+25w+w^2)=0}}}
w=5.7002747232013
*[invoke quadratic "x", 1, 25, -175]