If a hen and a half can lay an egg and a half in a day and a half, how long will three hens take to lay twelve eggs?

1.5 hens can lay 1.5 eggs in 1.5 days

3 hens can lay 3 eggs in 1.5 days
3 hens can lay 12 eggs in 6 days

double the hens would double the number of eggs without changing the time
multiplying the the time would multiply the eggs without changing the number of hens