$$ In its initial weeks, the coffee shop operates from $8$ am to $4$ pm daily, and averages about $100$ customers per day.

$$ Since the coffee shop has a variety of new and unique blends, customers usually take around $6$ minutes to decide and place their order.

$$ After ordering, customers move to a separate queue to wait for their beverage, which on average has $4$ people waiting. The average time to get a drink once at the counter is $2$ minutes.

$$ Occasionally, customers $($about $10\%$ of them$)$ ask to customize their beverage further, which can be done at the same station and generally takes about $20$ minutes. This is done without forming an additional queue$\mathrm{.}20$ minutes. There is no queue for this

On average, how many customers are being served at the pick$-$up counter?