. A certain professor used a non-traditional method to assign grades. The grades in the class were normally distributed with a mean of 72 and a standard deviation of 14. The lowest 10% received an F, the next 20% received a D, then the next 40% received a C, the next 20% received a B, and finally the top 10% received an A. What was the cutoff grade between the B's and C's?