Answer: 11 pounds
Explanation:
Total weight of the first 8 backpacks
8*14
= 112 pounds
Total weight of the second 12 backpacks
12*9
= 108 pounds
Total weight of the whole 20 backpacks
112+108
= 220 pounds
therefore the mean weight of the 20 backpacks is
220 / 20
= 11 pounds