Hi, there is something wrong when I tried the exercise as the same as Martin did.
thanks for reaching out! The Error you're getting says that the Numbers variable is not defined. To avoid the error you need to execute the cell above where you define the Numbers variable to be a list:
Numbers = [15, 40, 50, 100, 115, 140]
You can do so by clicking the cell and pressing SHIFT + ENTER, or you can use the Jupyter Notebook menu and click on the Run button. Then when you execute the second line it should be error free.
If you have any further questions, don't hesitate to write to us.