Question 155515
We have two sides a and b (length,width) but because b is just twice the a, we can express length of both sides using only one variable: a, 2a
after plugging in all the variables you should be left with quadratic equation in one variable.
Cheers,
Adam
p.s. If you don't know which equation should you plug into, think about one which contains both sides of rectangle and it's perimeter...