Answer
8 feet
Work Step by Step
$(2x+8)(2x+6)=48+72$
$4x^2+12x+16x+48 = 120$
$4x^2+28x+48=120$
$(4x^2+28x+48)/4=120/4$
$x^2+7x+12 =30$
$x^2+7x+12-30 =30-30$
$x^2+7x-18=0$
$(x+9)(x-2)=0$
$x+9=0$
$x+9-9=0-9$
$x = -9$ (we can't have a negative length, so this is not an applicable answer)
$x-2=0$
$x-2+2=0+2$
$x = 2$
This means the cement border should be 2 feet around all sides of the pool.
$6+2=8$
$8+2 =10$
