The number of cows and foxes in the yacht is 20+15 = <<20+15=35>>35
Mr. Bodhi also has three times as many zebras as foxes in the yacht, equal to 3*15 = <<3*15=45>>45 zebras.
The number of animals in the yacht so far is 35+45 = <<35+45=80>>80
To balance the yacht, Mr. Bodhi needs to add 100-80= <<100-80=20>>20 sheep
#### 20