Students of TO-007 prefer that the class ends no earlier and no later than 5 minutes before/after the time when it is supposed to end (let's call this time - time X). Based on historical data which includes previous years, the distribution of times when the class ends is normal with the classes ending on average 4 minutes later than the time X. Standard deviation of this distribution is 0.5 minutes. What is the sigma-capability of the professor