An elevator at a frequented school building is expected to operate for $60\mathrm{.}0$ hours after each repair. The mean repair time is estimated to be $5\mathrm{.}0$ hours. Determine the availability of the elevator?

a$.0\mathrm{.}8931$

b$.0\mathrm{.}0769$

c$.0\mathrm{.}8763$

d$.0\mathrm{.}9231$