Which subnet mask should you use?

[1237Aq]

You are working with a network that has the network ID 10.9.0.0 and contains 73 networks. In the next year, you will be adding an additional 27 branch offices to your company. For simplified management, you want to keep the most possible hosts per subnet. Which subnet mask should you management, you want to keep the most possible hosts per subnet. Which subnet mask should you use?

a. 255.224.0.0
b. 255.248.0.0
c. 255.254.0.0
d. 255.240.0.0

[Boss]

B or D I think.