$6\mathrm{.}9.$ An order for $250$ bell ringers is processed on work centers $10$ and $20.$ The setup and run times are as follows. It is decided to overlap the lot on the two work centers and to split the lot into two lots of $100$ and $150.$ Move time between operations is $30$ min$-$ utes. Work center $20$ cannot be set up until the first lot arrives. Calculate the saving in manufacturing lead time.

Setup on A $50$ minutes

Run time on A $=5$ minutes per piece

Planned backlog $=20$ units

Actual backlog $=18$ units