The 24 hats tell us that there are 24 total animals, so Reindeer + Snowbirds = 24 or R + S = 24.
The 38 pairs of boots. . . Reindeer have 2 pairs of legs and snowbirds have 1 pair of legs, so 2R + S = 38.
Now we have two equations:
2R + S = 38
R + S = 24
Let's write that first equation like this:
R + R + S = 38
But since R + S = 24 we can do this:
R + 24 = 38
R + 24 - 24 = 38 - 24
R = 14
There are 14 reindeer.
But since R + S = 24 we can do this:
14 + S = 24
14 - 14 + S = 24 - 14
S = 10
There are 10 snowbirds.
Answer: There were 10 snowbirds.
.
Check:
14 reindeer and 10 snowbirds would need 14 + 10 = 24 hats. Good.
14 reindeer and 10 snowbirds would need 14 * 2 + 10 = 28 + 10 = 38 pairs of boots. Good.