1. The problem statement, all variables and given/known data A rectangle is expanding so that its length is always twice its width. The perimeter of the rectangle is increasing at a rate of 6cm/min. Find the rate of increase of the area of the renctangle when the perimeter is 40 cm. 2. Relevant equations 3. The attempt at a solution p = 6x dp/dt = 6 dx/dt 6 = 6 dx/dt dx/dt = 1 40 = 6x x = 40/6 a = 2x^2 da/dt = 4x^3 dx/dt da/dt = 4(40/3)^3 (1) da/dt = 32000/27 However, this is not the right answer as the correct answer is 80/3 cm^2/min. Can anyone please help me solve this question? I have been stuck on it for the past half hour.