There are $3600$ baby chickens on a farm. The number of hens on the farm is $\dfrac{8}{9}$~of the baby chickens, and the number of roosters is $\dfrac{1}{16}$~of the number of hens. How many roosters are there on the farm? 
选项为:A:$$180$$  B:$$200$$  C:$$100$$  D:$$225$$  请回答其中一个选项.