Question 199699
area of building is 80m * 100m or 8000m^2


let x = "width of lawn"
so dimensions of building plus lawn are 80+2x by 100+2x


since the area of the lawn equals the area of the building,
(80+2x)(100+2x) = 2 * 8000


FOILing ___ 8000 + 360x + 4x^2 = 16000


subtracting 16000 and dividing by 4 ___ x^2 + 90x - 2000 = 0


use quadratic formula to find x