The element argon has three stable isotopes, 36 Ar, 38 Ar, and 40 Ar. 36 Ar has an isotopic mass of 35.968 u and an abundance of 0.34%. 38 Ar has an isotopic mass of 37.963 u and an abundance of 0.06%. 40 Ar has an isotopic mass of 39.962 u and an abundance of 99.60%. Calculate the average atomic mass of argon.