The formula of the area of a rectangle is A = LW
You have been given the length and width as (x+1) and (x+3). You've also been given the area, 80 ft2
So we can substitute what we have in the formula as follows
80 = (x+1)(x+3)
If we FOIL the right side of the equation, we have
80 = x2+4x+3
Let's bring the 80 to the right side of the equation so that we have an equation equal to 0.
x2+4x-77 = 0
We can factor this as
(x+11)(x-7) = 0
So,
x+11 = 0 This gives us x=-11 which would yield dimensions of -10 and -8. Since we can't have negative dimensions, let's check the other factor.
x-7=0, giving us x=7
So the dimensions of the porch are
(7+1) and (7+3)
The porch is 8 x 10