Use this figure and transformations to create a design on grid paper

This is very simple. You have 3 hens. They lay 3 eggs over 3 days. Well, make this easier on yourself. 1 egg=1 day. 

So, the answer would definitely be 12 days from 3 hens=12 eggs.

Unless of course, the question was implying the 3 hens lay 3 eggs EACH, over 3 days. Meaning by the 3 day period, you'd have 9 eggs, meaning one hen lays 3 eggs in 3 days.

So, multiply 9*4, since 3*4=12
9*4=36, so by the 12 day period you'd have 36 eggs, but this is only if the question is implying EACH

If not, then the answer is 12 eggs.

~Hope this helps!