On the calculation of $L=\frac \lambda{\mu-\lambda}$

Question

I have a question regarding the calculation of $L=\frac \lambda{\mu-\lambda}$

In the exercise, $\lambda=30$ and I think $\mu=30\cdot1$.

Am I right?

However this will lead to an indetermination in the denominator of $L$.

How should I prooced here?

Please help me.

This exercise is from Operational Research by Hillier

Answer 1

No, the value of $\mu$ is $60/1.5=40$ per hour for the current system.