Data:
Organice the data from least to largest:
From 7.0 to 7.9

From 8.0 to 8.9

From 9.0 to 9.9

From 10.0 to 19.9

From 11.0 to 11.9

From 12.0 to 12.9

From 13.0 to 13.9

To make the frequency distribution you need to stablish the groups in millions of people, and then count the number of data that fit in that data range.