Please help me understand this business analysis 2372 homework. Step by step would really help. Serum cholesterol levels in the American adult

Please help me understand this business analysis 2372 homework. Step by step would really help.

Serum cholesterol levels in the American adult population have a bell shaped distribution like the one shown below. The mean is 213 and the standard deviation 7. A "healthy" level is one that falls within the range of 95% of all cholesterol levels. Use the 68-95-99.7 rule to determine the highest "healthy" cholesterol.