Answer
10 ft by 25 ft
Work Step by Step
$x(2x+5) = 250$
$2x^2 +5x= 250$
$2x^2 +5x-250 = 250-250$
$2x^2 +5x-250 =0$
$2x^2-20x+25x-250 =0$
$2x(x-10)+25(x-10) =0$
$(2x+25)(x-10)=0$
$2x+25=0$
$2x+25-25 = 0-25$
$2x = -25$
$2x/2 = -25/2$
$x = -12.5$
$x-10=0$
$x-10+10 = 0+10$
$x = 10$
We can't have a negative length, so $x\ne-12.5$.
$2x+5$
$2*10+5$
$20+5 =25$