You can
put this solution on YOUR website!50*70=3500 sq feet thus the border must be 3500-2400=1100 sq feet or
(70-2x)(50-2x)=2400 or 3500-100x-140x+4x~2=2400 or 4x~2-240x+1100=0 or
x~2-60x+275=0 or (x-55)(x-5)=0 or x=55 & X=5 THUS THE SIDEWALK IS 5 FEET WIDE