On day 23, our focus is on Histograms which is a special 'Bar' chart for grouped data and will often have different widths. Beware the trap that the y axis is NOT frequency but should be labelled frequency density. The formula for calculating frequency density is covered in this snapshot and you may need to create extra columns in order to calculate this.
By rearranging the formula, you can calculate the frequency of each bar by multiplying frequency density by the bar width. This will help to fill in an incomplete data table.