The correct answer is C. (5x+3) feet, and here is how I got it. This is the equation you need to use: (a+b)^2 = (a+b) (a+b) So, let us plug in 5x and 3 here: (5x+3)^2 = (5x+3)(5x+3) = 25x^2 + 15x + 15x + 9 = 25x^2 + 30x + 9 which is the area of the garden.
