Using the following graph to find the mean, median, and mode.

Given the following set of data, find the mean, median and mode(s),
respectively.
{19, 23, 25, 29, 31, 29, 25, 25, 19, 21, 17, 21, 27, 23, 21, 33, 25, 15, 21, 33, 29, 31}