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