One teacher involved 
Teacher Hugo takes a total of four classes for lesson number 76. This means that each class 'uses' a quarter of the teacher. For this reason the lesson with two weekly periods has a value of 0.5 from the perspective of class 1a
The situation can be calculated as follows:
(number of weekly periods) / (number of classes) = (value)
Using the example of lesson 76, this would be:
2 / 4 = 0.5
