The standard error (SE) is the standard deviation of the sampling distribution of a statistic.
The relationship between the standard deviation of a sample drawn from a population with the standard deviation of the population is defined such that, for a given sample size, the standard error equals the standard deviation divided by the square root of the sample size.
Therefore, the formula that would produce an estimate for the standard error of the sample is "Divide the standard deviation of the sample measures by 8". [8 is the square root of 64].