Excellence Middle School charges $6.25 for students from all grade levels to attend the school dance. If S represents the number of seventh grade students who came to the dance and g represents the number of eighth grade students at the dance, which expression BEST represents the total money collected for attending the dance.

a. 6.25s + g
b. 6.25(s + g)
c. 13.50(s + g)
d. 6.25(s + g)