Please help me deal with this questions. Thank you so much.

Problem 6 A system consists of three independent components, A, B and C, connected in a series. The lifespans of components A, B, and C have an exponential distribution with parameters 0.2, 0.1, and 0.15 (days)'1 (equivalently, means 5, 10, and 1/015 days). The system fails when one of the components fails. (a) Find the probability that the component whose failure caused the system to fail is 1 2 component C. (b) You can increase the expected lifespan of one of the components by 1 day. Which component should you select for this improvement in order to cause maximal possible increase in the expected lifespan of the entire system