The ratio ...
... seniors : juniors = 3 : 2
can be multiplied by 7 to get
... = 21 : 14
indicating there are 14 juniors for the 21 seniors in the choir.
50:40=x:35
5/4=x/35
times both sides by (4*35)
5*35=4x
175=4x
divide both sides by 4
43.75=x
costs $43.75
Answer: B seems to be the correct one