Consider a unit in a mission time of 400. Four units are tested:In test A, a unit fails at time 1=445.87;In test B, a unit fails at time 2=188.93, then repairs after a period of time 2=346.18;In test C, a unit fails at time 3=388.65, then repairs after a period of time 3=24.46;In test D, a unit fails at time 41=319.20, then repairs after a period of time 4=50.81; after working for another period of time 42=163.51, the unit fails again.

(1) Calculate the unit reliability and instantaneous availability at time 300;

(2) Calculate the unit reliability and instantaneous availability at time 400;

(3) Calculate the unit average availability over its mission time.