A particular computer game involves the capturing of three types of mythical creatures: Arps,

Question

Orps and Urps.
Arps have 6 legs, 3 horns and a tail.
Orps have 4 legs and 2 horns, but no tail.
Urps have 3 legs and a tail, but no horns.
The last time Billy played this game he captured 45 creatures with a total of 222 legs, 99 horns
and 33 tails.
How many of the 45 creatures that Billy captured were Urps?

Answer 1

a+o+u = 45
6a+4o+3u = 222
3a+2o+0u = 99
1a+0o+1u = 33
You have 4 equations in 3 unknowns, so I hope they are consistent.

Answer 2

20