You have already found the slope, which is 2
m =( y2-y1)/(x2-x1)
= (9200-9000)/(225-125)
= 200/100
= 2
The question tells us that it is a linear function
y = mx +b is the slope intercept form of a linear function
m is the slope and b is the initial value
c(n) = mn+b
c(n) = 2n+b
Using one of the points in the table we can find b
(125,9000)
9000 = 2(125) +b
9000 = 250+b
9000-250 = b
8750 = b
The initial value is 8750
This is also the estimate of c(0) because the initial value is when n=0
We can write the equation
c(n) = fixed cost + unit cost * number of units
The fixed cost is the initial value
the unit cost is the slope or m
c(n) = 8750 + 2n