This is almost identical to numerous other threads you have posted in the last few weeks. What exactly are you struggling with?

The CDF of the exponential distribution is:

so

So, the probability that the first component is alive after 1000 hours is

similarly for X2, and X3 :

You want P(X1 and X2 and X3 alive after 1000 hours)

Part b

You want to find F(K) = P(system fails by time K)

So

1-F(K) = P(system still alive at time K)

You can easily find the right hand side by generalising your answer to part a.