There are 4 more Muscovy ducks than Cayugas, and 3 more than twice as many Cayugas as Khaki Campbells. If there are 90 ducks total, how many Muscovies are there?
Let's think step by step below.
39
Let x represent the number of Khaki Campbell ducks.

Cayugas:3 + 2x.

Muscovies:4 + (3 + 2x) = 7 + 2x.

Total: x + 3 + 2x + 7 + 2x = 90.

5x + 10 = 90.

5x = 80.

x = 16.

Muscovy: 7 + 2(16) = 39.

.

So, the answer is 39