Answer:
The interval that contains the middle 68% of the heights is from 52 inches to 60 inches.
Explanation:
The empirical rule states that, for a normally distributed variable:
The middle 68% of the measures are within 1 standard deviation of the mean.
The middle 95% of the mesures are within 2 standard deviations of the mean.
The middle 99.7% of the measures are within 3 standard deviations of the mean.
In this problem, we have that:
Normally distributed with mean 56 inches and standard deviation 4 inches.
So the interval that contains the middle 68% of the heights is from 52 inches to 60 inches.