A.
In order to calculate the number of bags per week, calculate the quotient between the number of pounds per week and the pound of one bag of flour:
number of bags = 350 lb/50 lb = 7 bags
Hence, you need 7 bags per week
B.
The cost of 7 bags is:
cost = $0.79 * 7 = $5.53
Hence, you spend $5.53 in flour