From the given problem,
length is twice as long as the width
length = 2 x width
Note that the perimeter is :

where W and L are the width and length respectively.
Since L = 2W
Perimeter will be :

Perimeter is equal to 30 inches :

From the given choices, only B satisfies this condition.
2W + 2W + W + W = 30
6W = 30
Therefore, the answer is B.