A builder uses the rule "Multiply the number of trusses needed by 50 to get the length of a roof." If 8 trusses are needed to build a roof of length 400 inches and 10 trusses are need to build a roof of length 500 inches, how many trusses are needed to build a roof of length 250 inches?

A.
4 trusses

B.
5 trusses

C.
6 trusses

D.
7 trusses