I really need help in subnetting for a school project

Hello,

We have a school project in groups of 3 going on where we have to lay out a company's assets, network and its simulation for which we will get an important mark. I have the task to calculate the hosts/subnets.

Im really confused since like 2 days because of this following task:

3 rooms: 150 host's in Development, 50 host's in Marketing and 50 host's in Selling. Total 250

I have to create 3 subnets ( because 3 rooms?, not sure) out of this with 2 extra subnets to fall back on if something is going wrong.

So now im really confused as to what exactly i should do or how i should do it. 250 Host's fit into the C Class but the subnets would be way too small for each room because of the 150 Room. I think i need to create 8 subnets because of 5 -> 8.

But if I create a B Class Network the company would have toooooo many adresses without any hosts to fill it. But is this the only way to do this?

I really hope some of you could help me with this. Im really lost and i need atleast a point into the right direction. Thanks in advance!