I hope it is a quick one :) I just can't find the formula. Section 6.

Hi. I hope it is a quick one :) I just can't find the formula.

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