The meaning of the first underline: buy B insurance but not A insurance, so it should be the probability of buying B multiplied by the probability of not buying A, that is, p×( 1-0.5), so as to get P.

The meaning of the second underline: the opposite event of buying at least one kind is that the probability of not buying both kinds is (1-0.5)×( 1-0.6), and subtracting from 1 is the probability of demand, namely 1-( 1-).