The failure time (in hour) of a component is lognormally distributed with parameters t = 4 and t = 0.9.

a. What is the MTTF for this component?

b. When should the component be replaced, if the minimum required reliability for the component is 0.95?

c. What is the value of the hazard function at this time (i.e., for the time calculated in part (b))?

d. What is the MRL at this time if the component has already survived to this time (i.e., for the time calculated in part (b))?