$8.$ How many $$l of a $100$ mg ml$-1$ solution of ampicillin would be required to be added to $20$ ml of liquid cell growth medium to give a final concentration of ampicillin of $50$g ml$-1?$

a$.$ First work out how many $\backslash$mu g in total $($in $20$ml$)$ are needed.

b$.$ How many microlitres of the $100$ mg ml$-1$ solution of ampicillin are needed?