My second attempt:
Number of girls: 7
Number of backpacks: 49
Number of big cats: 343
Number of small ones: 2401
Number of legs for girls: 7 * 2 = 14
Number of legs for big cats: 343 * 4 = 1372
Number of legs for small cats: 2401 * 4 = 9604
Total legs = 14 + 1372 + 9604
=
10990
But! Assuming that the small cats aren't actually there (you didn't specifically say so):
Total legs = 14 + 1372
=
1386
Gotta be right unless it's an extra-annoying trick question.
[edit]
But, assuming that the girls didn't bring their backpacks, because you didn't specify that either:
Total legs =
14
Ok, gotta be one of the above
Don't you just hate that Zotoaster guy?