Final answer:
Brian can load 12 boxes into the truck.
Step-by-step explanation:
To find out how many boxes Brian can load into the truck, we need to subtract the weight of the cargo already loaded from the maximum weight the truck can carry. The maximum weight the truck can carry is 1480 pounds and Brian has already loaded 640 pounds. So, the remaining weight the truck can carry is 1480 - 640 = 840 pounds.
Since each box weighs 70 pounds, we divide the remaining weight by the weight of each box to find out how many boxes Brian can load. So, 840 ÷ 70 = 12 boxes.
Therefore, Brian can load 12 boxes into the truck.