When adding the cost of contribution as in the example in the free notes, we added the variable selling cost of 1$ that represents the variable cost of selling one unit. However what I don’t understand is why do we multiply the variable selling price by 9000 at a later stage if we already added it up to the cost of contribution? If we were to multiply it by 9000 which I understand, then we shouldn’t we have added it to the contribution? Or am I being thick here.
You asked this as a comment on the lecture, and I answered you there.
The $1 is not anywhere added to the contribution. It is an extra cost and therefore reduces the contribution. It is multiplied by 9,000 because it is a variable selling cost and 9,000 units were sold.