The area of a rectangle is 85 square feet. the length is 12 feet longer than the width. find the length and width of the wall

Formula for area of rectangle:
A=L x w
Here A=85 square ft
Length, L=w+12

Put values in formula.
85=(w+12)w
85=w^2+12w
Subtract 85 from both sides
w^2+12w-85=0
Factorise the equation.
(w-5)(w+17)=0
w=5 and w=-17
Ignore the negative value of width.
Width, w= 5 ft  and Length, L=12+5=17 ft

Width=5 ft and Length=17 ft