Marginal cost $60; 120 items cost $9500 to produce. The linear cost function is

C (x) = $60 + ($79.17/unit) x

Step-by-step explanation:

The linear cost function is represented by a straight line with slope $60/unit and y-intercept $60:

C (x) = $60 + ($9500/120 units) x, or

C (x) = $60 + ($79.17/unit) x