Question 881994
A1 = area of garden including the border (w) = (7+w)*(12+w)
A2 = area of garden = 7 * 12 = 84
Area of border = (7+w)*(12+w) - 84 = 92
(7+w)*(12+w) = 176
w^2 + 19w + 84 = 176
this is a quadratic equation
w^2 + 19w -92 = 0
factor this equation
(w-4) * (w+23) = 0
w is 4 or -23
our answer has to be w > 0, so w = 4 m