( 6 + x)(9 + x) =88
54 + 15x + x^2 = 88
x^2 + 15x - 34 = 0
(x + 17)(x - 2) = 0
using zero product property:-
x + 17 = 0 or x - 2 = 0 giving:-
x = -17 , x = 2
x is the amount that the length and width are increased by.
x = -17 is negative and doesn't make sense in this context and can be ignored; so the amount of increase is 2 feet.
Although it is a straight line it does not pass through the origin or (0,0) so it is NOT a proportional relationship.
