The line plot shows each thumb length and the number of people that has each thumb length. From the line plot, the longest thumb length is owned by only one person and it is 2 3/4 inches. The shortest thum length is 1 2/4 and it is owned by only one person too. We would find the difference between these thumb lengths.
Converting both lengths to improper fraction, we have
2 3/4 = 11/4 inches
1 2/4 = 6/4 inches
Difference = 11/4 - 6/4 = 5/4
Converting 5/4 to mixed fraction, we have 1 1/4
Thus, the difference between the longest and shortest thumb nails is 1 1/4 inches