A and C are the only ones who could work...
Because 16+16=32 2+2=4 so 4 counselors to 32 campers
16+16+16=48 and 2+2+2=6 so 48 campers to 6 counselors could also work.
Is the table attached to the question
The bill is issued on the 3rd.
It is due 8 days later, this means that it is due on the 11th.
There is a one day grace period.
Since Frank paid the bill on the 12th, this means that his payment is received after the deadline. However, he will not be charged for any extra fees as he was still in the grace period when he paid.