You basically have to count how many days received the amount of mail listed in the left column. Then out of the total amount of mail received, you would compute the fraction of the days during which a given amount of mail was received.
For instance, on every day, at least 5 pieces of mail were counted, so there are 0 days on which 0-4 pieces of mail were received.
On the other hand, on days 5-7 (15, 18, 19), the amount of mail received fell within the 15-19 range. This means out of 7 days, 15-19 pieces of mail were received on 3 of those days. So the frequency with which this occurred was [tex]\dfrac37\approx0.43[/tex].
So what you should get in the right column is
[tex]\begin{matrix}0-4&|&\frac07=0\\\\5-9&|&\frac27\approx0.29\\\\10-14&|&\frac27\approx0.29\\\\15-19&|&\frac37\approx0.43\end{matrix}[/tex]
