How to Draw and Read a Box Plot

The range is the difference between the maximum value (80) and the minimum value (20): $80-20=60$.

The interquartile range is the difference between $Q_3$ and $Q_1$. From the boxplot, $Q_3=60$ and $Q_1=30$, so $60-30=30$.

The median is shown by the line inside the box, which corresponds to the value 50 on the scale.

The middle $50\%$ of the data lies between $Q_1$ and $Q_3$. From the boxplot, these are 30 and 60.

From $Q_1$ to $Q_3$ accounts for $50\%$ of the data, and from $Q_3$ to the maximum accounts for another $25\%$. Together, this makes $75\%$.

The minimum value is 10 and the maximum is 80. The median is 40. The lower half ($10,20,35$) has a median of 20 giving $Q_1=20$. The upper half ($45,70,80$) has a median of 70 giving $Q_3=70$.