If X∼N(10,4)X \sim N(10, 4)X∼N(10,4) and Y∼N(5,9)Y \sim N(5, 9)Y∼N(5,9) are independent, what is the standard deviation of W=X−YW = X - YW=X−Y?
13\sqrt{13}13
5\sqrt{5}5
555
131313