Here is a problem I don't understand how to solve.

PROBLEM: The weight of a randomly selected bag is a random variable with mean = 25 pounds and standard deviation = 1 pound. The weights of bags are independent from each other.

1)What is the standard deviation for four times the weight of ONE bag that is randomly picked? (2, 4, 8 or 16 pounds)

2)What is the standard deviation of the sum of the weights of the FOUR bags that are randomly picked? (2, 4, 8 or 16 pounds)

I don't understand how to add the standard deviations in both cases.

Thank you for your help