Linear Modeling
Two variables y and x are said to be modeled by a straight line if the relationship between them is written as:
y = mx + b
Where m and b are constants.
In this case, C is the dependent variable and x (the number of units) is the independent variable, thus:
C = mx + b
We know each unit costs $1 to produce. This is the variable part of the equation. A total of $2000 are needed as a fixed amount of money regardless if we produce 1 or 100 units.
That is the fixed or constant part of the equation.
Joining these concepts, the required formula is:
C = 1*x + 2000
The number 1 can be omitted:
C = x + 2000
Now the graph is shown below: