*x*) like this: y = k

*x*, where k is a constant

However, I am not so sure if this makes sense in job costing:

For example, for job A, we need 1 worker to work for the basic number of hours (40 hours/week) for 1 week, plus overtime in that week.

Basic rate is £8 an hour. Overtime is time and a half (£12 an hour)

Then:

Let

*x*be the number of labour hours worked, where

*x*is greater than or equal to 40

Am I correct to say that the graph for the total labour cost (y) is:

y = 8 x 40 + 12 (

*x*- 40) = 12

*x*- 160?

Then, the graph does not have the form y = kx, so the total labour cost here is no longer a variable cost, which seems strange?