Annoying ceiling/floor word problem :(

mr. smith is bringing in bagels for his class. The bagels are sold in dozens. Each dozen costs 6.99. if mr.smith can not buy smaller quantities write an equation that will represent the number of bagels, B he will need, if he has S students in his class and D dollars.

I'm normally pretty good at these, but it's like this one seems to have an extra variable that is messing me up.

I know its d= 12 then a negative floor function i believe but i am unssure. any help is appreciated.