Question 4 (25 marks). An insurer has the following portfolio of policies: The insurer purchases reinsurance with a retention limit R(R>1) per policy at a cost of 0.025 per unit of reinsurance coverage. (a) Write down the retained risk S and the cost of reinsurance C in terms of R. (b) With the normal approximation, determine R to minimize the probability that the sum of the retained claims and the cost of reinsurance exceeds 36