In order to find the mode, you have to rearrange the numbers to be least to greatest.
7, 9, 9, 12, 12, 14, 15, 17, 17, 18, 18, 18, 20, 21, 23, 26
Now you want to find the mode of the weights, or set of numbers.
The mode is the most frequently occuring value (or values) in a set of data. A data set may have no mode, one mode, or more than one mode.
So, the most occuring number(s) are/is 18.
One 7, 14, 15, 20, 21 23, 26.
Two 9's, 12's, 17's.
Three 18's.
So, 18 is the mode of these weights.
Hope this helped,
-Anime