Descriptive Statistics: Box Plot Construction and Interpretation

The stem-and-leaf diagram shows the masses of \(21\) students.

1. Write down the modal mass.
2. Calculate the percentage of the students who weigh at least \(55\text{ kg}\).
3. The box-and-whisker plot for the above distribution is shown below. Write down the value of \(a\) and of \(b\).

Box-and-whisker plot for mass distribution