So 7 girls with 7 backpacks = 49 backpacks
7 girls with 2 legs each = 14 girl legs
7 big cats in each backpack(49 of them) = 343 big cats
343 big cats with 4 legs each = 1372 big cat legs
343 big cats with 7 little cats each = 2401 little cats
2401 little cats with 4 legs each = 9604 little cat legs
14 girl legs + 1372 big cat legs + 2401 little cat legs = 10990 legs
However, if there is a bus driver, it’s 10992.