To calculate Peter's new grade after not doing an assignment worth 100 points, you need to know how the assignment contributes to the overall grade. If the assignment is worth a certain percentage of the total grade, you can calculate the new grade using the following formula:
New Grade = (Previous Grade * Weight of Previous Work) / (Total Weight)
However, if you don't have information about the weight or percentage of the assignment, it's not possible to determine Peter's new grade accurately. Please provide more details about how the assignment affects the total grade, and I can help you calculate the new grade accordingly.