Show me the steps to solve $20.$ Two machining operations A $(3$ minutes per part$)$ and B $(10$ minutes per part$)$ are performed sequentially to manufacture a part. Machines A and B produce $\backslash (5\backslash \%\backslash )$ and $\backslash (6\backslash \%\backslash )$ defective items, respectively. The factory operates $8$ hours each day, $5$ days per week, $4\mathrm{.}2$ weeks per month. Every day each machine needs $0\mathrm{.}30$ hours for being set up$.$ Find the machine fraction for each type $($A and B$)$ if we need to handle a demand of $1,000$ items per month? Use a machine$-$up factor equal to $\backslash (85\backslash \%\backslash )$ for each machine.