Which term of the AP: 3.8, 13, 18,is 78?

Given a circle with a radius of 4, which is the circumference

Kevin is an insurance salesman. when he sells a policy, he makes 20 percent of the policy premium (p) up front; then each year the policy is active, he receives 15 percent of the original premium. which equation could be used to figure his total commission on a policy that has been active for five years? c=0.80p c=0.20p + 0.15p c=0.35p + 4(0.15) c=0.95p

Can someone me with this problem . show your work .