I'm trying to pick up an old exam that's been left hanging, needless to say my math is a bit rusty. I came across the following problem and don't remember how to handle components that already has a run time different from t0.

The problem at hand:

Two components that are coupled in series in a block diagram have a ware-out distribution which is a Weibull distribution with shape factor 2. The t0 = 1000 hours. The mean time to failure for both is 3000 hours. One of them has run 1000 hours and the other 1500 hours. Calculate the probability for the system to survive the next 10 days (=240 hours).

How is the probability calculated for the component with the run time of 1500 h? The answer to the whole problem would also be deeply appreciated!