(b)

the probability of observingexactlythose hours is zero, because its a continuous variable.

Presumably the question means (what is the probability that you'd observe a disk with less than 1.6, then a disk with less than 2.8, then a disc with less than 3.1

In this case just multiply your probabilities together.

that should enable you to answer (c). Because part (b) is effectively a hypothesis test.