Write a function, average_peer_pressure, which takes in a month, and returns a vector of length two. For the first element, consider doctors who began prescribing in that month, then return the average proportion of prescribers among their contacts. For the second element, consider doctors who began prescribing after that month (or never did), then return the average proportion of prescribers among their contacts. Call your functions from (2) and (5); use a function from the apply family rather than a loop if at all possible. Check that month 5 returns 0.2698052 and 0.525822. (Hint: mean has an na. rm option)