Starbucks employs one worker to make both espresso drinks and to pour drip coffee.

Starbucks employs one worker to make both espresso drinks and to pour drip coffee.  On average, an espresso drink takes 4 minutes to make and drip coffee takes 1 minute to pour.  The number of customers that order espresso drinks is 6 per hour and the number of customers that order drip coffee is 18 per hour.  What is the utilization of the Starbucks coffee employee?