Hi. I hope it is a quick one 🙂 I just can’t find the formula.

Section 6.1, Exercise 4

Data accumulated by the National Climatic Data Center shows that the average wind speed in kilometers per hour for Perth, is 9.7. Suppose wind speed measurements are normally distributed for a given geographic location. If 22.45% of the time the wind speed measurements are more than 11.6 kilometers per hour, what is the standard deviation of wind speed in Perth?

Round your answer to 1 decimal place, the tolerance is +/-0.1