Question $3$: $[5$ marks: $2\mathrm{.}5$ marks each$]$

In a binary multiplier that multiplies an n$-$bit $($first number$)$ by m$-$bit $($second number$)$ binary numbers,

a$.$ How many k$-$bit adders are needed?

b$.$ How many ANDs, external to the k$-$bit adders are needed?