Amy's grade was the 90th percentile of the 80 grades for her class. Of the 100 grades from another class, 19 were higher than Amy's,and the rest were lower. If no other grade was the same as Amy's grade, then Amy's grade was what percentile of the grades of the two classes combined?


a) 72nd
b) 80th
c) 81st
d) 85th
e) 92nd



Please provide your answer with the working.