You were hired to analyze the results of the grade 10 literacy tests. There are 12,000 children in your region to be tested. A few weeks later the test your supervisor calls you and asks what the mean score and standard deviation was in your region. You do not have your calculations with you but you do remember that the test results were normally distributed and that your son got a score of 138 and his score was 2.1 standard deviations above the mean. You also recall that the mean was 127. 

What was the standard deviation for students in that region?