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