Inspired by book problem $13\mathrm{.}11$: An average corrective maintenance time of $1$ hour or less has been assigned to system ABC. Allocate the fractions of an hour to the assembly of the system using the data in the following table:

Assembly Quantity lambda Avg. Mct

A $10\mathrm{.}052$

B $20\mathrm{.}160\mathrm{.}6$

C $10\mathrm{.}270\mathrm{.}9$

D $10\mathrm{.}121\mathrm{.}5$

Determine the assembly average Mct$.$