Poisson process: phone calls

We assume that phone calls arrive according to a Poisson process with rate 2. If I know that up to time t = 1 there is one call only, how likely is it that it arrived after t = 0.75? If I know that up to time t = 1 two calls arrived, how likely is it that the second arrived after t = 0.75?

So for the first problem I set that
P(S1>0.75/X(1)=1), with S1, the time it takes for the first event to occur, and X(1), the number of events that occurred up to time 1. But then I don't quite see how to handle it.
Write the formula for conditional probability and then use the fact that increments of a Poisson process on non-overlapping intervals are independent.