Hens, eggs, days

If a hen and a half lay an egg and a half in a day and a half then how many hens will it take to lay six eggs in six days?

no of hens directly propotional to eggs and inversely propotional to days

 x     1.5       6
--- = -----  x  ----
1.5     6        1.5
       ^^^       ^^^
       days      eggs

x = 1.5