The city of Boston decided to reconstruct its major tunnels. It estimated the job would require 612 mini projects spread evenly over an 18-month plan of completion. Only 108 mini projects had been successfully completed after 6 months. At this time, the construction was behind schedule by how many projects?

A. 34
B. 96
C. 198
D. 204
E. 504

OA is B

OA says B I got A what could be the answer. An Expert pls. Thanks