Yeah, it is. Its really obvious because x 1 is supposed to be negative which cancels out the middle to leaving A or D. x 3 is positive, and its positive on the first chart so the answer's the first one.
if he bought three bags of gravel that are 20 lbs. each then he would have 60 lbs. of gravel. In the end he only had 7 pounds left so you would subtract 7 from 60 and get 53 pounds.
