Imagine that you are an investor who has to decide between two types of businesses $($e$.$g$.,$ restaurants$)$ to make your investment. Both businesses have the same average arrival time and the same average service time, but their distributions are different:

Business $1$: Customers arrive at a rate of $15$ per hour and it takes an average of $2$ minutes to provide the service to the customer. There is only one server. Interarrival times and service times are exponential.

Business $2$: Customers arrive at a rate of $15$ per hour and it takes an average of $2$ minutes to provide the service to the customer. There is only one server. Distribution of interarrival time and service time are neither exponentially nor deterministic. The interarrival time has a standard deviation of $2$ minutes and the service time a standard deviation of $2$ minutes as well.

What is the average waiting time $($in min$)$ in line of customers at Business $2?$

Correct answer is $1\mathrm{.}25,$ how to get this number? Please show me the step