Answer: C.
There are 215 total students in the band.
There are 27 seniors in the band.
The probability is found by dividing the number of seniors in the band by the TOTAL number of students in the band.
P(S|B) = 27/215 = 0.1255813953
You have to round off the answer too the nearest tenth.
P(S|B) = 0.13