Answer:
14.85 feet & 18.85 feet
Explanation:
This is a rectangle with area 10 * 14 = 140 sq. ft.
We want new rectangle to be DOUBLE this area, so that area would be:
140 * 2 = 280 sq. ft.
We will add same amount, x, to both length and width, to get 280. Lets do this and find x. [note: length * width = area]
Area = length * width
280 = (10+x)*(14+x)
280 = 140 + 10x + 14x + x^2
0 = -140 + 24x + x^2
We can solve this by using middle term factorization:

So, we need to add around 4.85 feet to both length and width
New dimensions are 14.85 feet & 18.85 feet