Use the Empirical Rule. The mean speed of a sample of vehicles along a stretch of highway is 68 miles per​ hour, with a standard deviation of 4 miles per hour. Estimate the percent of vehicles whose speeds are between 64 miles per hour and 72 miles per hour.​ (Assume the data set has a​ bell-shaped distribution.)

Approximately ____​% of vehicles travel between 64 miles per hour and 72 miles per hour.