Answer:
42 = the number of hats Paula can knit from one yard of yarn
Step-by-step explanation:
The way this problem is written, the constant 42 is the multiplier of yards to get hats. That is, it has units of hats per yard, so represents the number of hats that can be knit from 1 yard of yarn.
_____
Comment on the problem
It seems more likely that the proportion should be written as ...
y = 42h
or
h = y/42
Then the constant would be the number of yards of yarn required for each hat.