Diana's parents keep a chart on the wall where they mark how much Diana grows each year. When Diana was 15, she grew 5/6 of an inch and when she was 16, she grew 1/3 of an inch. In total, how much did Diana grow in during those two years?
a. 1 and 1/2
b. 1 and 1/6
c. 1/2
d. 3/6