So
P = I – C
= sx – (a + bx)
= (s – b) x – a (3)
We now have a mathematical model of the relationships (1)  to  (3) between
the variables x, C, I, P, a, b, s These variables may be classified as:
independent
x
dependent
C, I, P
parameters
a, b, s
The manufacturer, knowing x, a, b, s can determine P Step 3 From (3), we can observe that for the break even point (i