The extent getting calculated is the same as shown in the tutorial. Please follow the steps properly as mentioned in the tutorial.
The extent value displayed in the tutorial is 20.043 for which the unit is not displayed. But the unit associated with the value 20.043 is mol/s whereas what you get is 72.1533 kmol/h which is equivalent to 20.043 mol/s. It was a bug in the earlier version (in which this tutorial was recorded) where the units of the extent were not displayed but now the bug doesn't exist anymore. You can cross-check the value in mol/s by changing the system of units to SI and re-run the simulation.