Explanation:
Let the breadth (b) of a rectangle be x
Then Length (L) = 2x
Now
Perimeter of the rectangle = 15 inches
Or, 2(L + b) = 15
2 ( 2x + x) = 15
2* 3x = 15
6x = 15
x = 15 / 6
x = 2.5 inch
Also Now
Length (L) = 2*2.5 = 5 inches
Breadth (b) = 2.5 inches
Hope it will help :)