A professional organization (for statisticians, of course) sells term life insurance and major medical insurance. Of those who have just life insurance, 70% will renew next year, and 80% of those with only a major medical policy will renew next year. However, 90% of policyholders who have both types of policy will renew at least one of them next year. Of the policyholders 75% have term life insurance, 45% have major medical, and 20% have both.
a. Calculate the percentage of policyholders that will renew at least one policy next year. 

b. If a randomly selected policyholder does in fact renew next year, what is the probability that he or she has both types of policies?