Check: probabilities total to 1, so all eventualities are covered.
a) We need to add the probabilities of 3 and 4 storms=0.11+0.04=0.15.
b) Given that there have already been two storms, the probability of 4 more storms means 6 storms in total. Let A=0.01 be the probability that 6 storms will occur and B=0.24 be the probability that 2 storms would occur. The probability that 6 storms will occur given that 2 have already occurred=
P(A⋂B)/P(B)=0.1/0.24=5/12=0.42 approx. because P(A⋂B)=P(A) since A includes B (6 storms includes there being 2 storms).
c) The total of all the given probabilities=1, so there is no probability for 7 storms. P(7)=0.