I've worked through a set of practice questions and ran across this problem and don't see how I can solve it without $\displaystyle \sigma$. Can someone please give me some direction?

Q: When someone dials 911 for an emergency, the average length of time to reach an operator is supposed to be no more than 30 seconds. However, in a recent survey of 81 such calls, the sample mean came out to be 32 seconds. Is the response time in fact too long? Use $\displaystyle \alpha$=.10

So, $\displaystyle \mu_0$=30, $\displaystyle n$=81, and $\displaystyle \bar{x}$=32.

$\displaystyle H_o$:$\displaystyle \mu=30$, and

$\displaystyle H_a$:$\displaystyle \mu>30$.

I wanted to use the Z or T test statistics but I guess I can't because I don't see that I'm provided with enough information to be able to use them.

I really appreciate your help! I'm sure there is something basic that I'm not seeing.