Farmer John has hens, geese, ducks, and 2 goats. The number of hens equals the number of geese and ducks combined. There are 5

Farmer John has hens, geese, ducks, and 2 goats.  The number of hens equals the number of geese and ducks combined.  There are 5 fewer geese than ducks.  If the total of animals is 40, how many are ducks?