Consider a unit in a mission time of 400. Four units are tested: In test A, a unit fails at time T1=445.87; In test B, a unit fails at time T2=188.93, then repairs after a period of time AT2=346.18; In test C, a unit fails at time Tz=388.65, then repairs after a period of time ATZ=24.46; In test D, a unit fails at time T4=319.20, then repairs after a period of time AT1=50.81; after working for another period of time AT2=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. Consider a unit in a mission time of 400. Four units are tested: In test A, a unit fails at time T1=445.87; In test B, a unit fails at time T2=188.93, then repairs after a period of time AT2=346.18; In test C, a unit fails at time Tz=388.65, then repairs after a period of time ATZ=24.46; In test D, a unit fails at time T4=319.20, then repairs after a period of time AT1=50.81; after working for another period of time AT2=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