I dont understand this problem I'm not sure if I should multiply or divide Dedra bought 3 metal balls. All together, the balls weighed 0.9 pounds. How much, on average, did each ball weigh?

The total weight of all three balls is 0.9 pounds, so each ball must have weighed less than the total. The advantage weight per ball would be represented by the ratio of total weight to quantity of balls measured:

(0.9 pounds) / (3 balls) = 0.3 lbs/ball