Answer:
Rectangle A's length = 22 ft., Rectangle B's length = 44 ft.
Explanation:
Since we know that the length of Rectangle B is twice the length of Rectangle A, we know that 2*(3x + 7) = Rectangle B's length.
We must set this equation to the dimensions already given for Rectangle B, which gives us 2(3x + 7) = 2 (5x - 3).
Using the distributive property gives us 6x + 14 = 10x - 6 and solving for x gives us x = 5.
We must plug five into the original dimensions to find that the lengths of Rectangles A and B are 22 feet and 44 feet respectively.