Q.A company's total cost function is $C(x) = 2500 + 45x$, where $x$ is the number of units produced.

C(x) is a linear function of x; the constant term is the fixed cost and the coefficient of x is the variable cost per unit. …

1. Fixed and variable cost. $C(x) = 2500 + 45x$ is linear in $x$ (intercept $2500$, slope $45$). The fixed cost is the cost incurred even at zero output, $C(0)=2500$, i.e. ₹2,500. The variable cost per unit is the coefficient of $x$, i.e. ₹45 per unit.
2. Total cost of 80 units.

   $C(80) = 2500 + 45(80) = 2500+3600 = ₹6{,}100$

3. Average cost per unit. $\overline{C}(80) = \frac{C(80)}{80} = \frac{6100}{80} = ₹76.25$ …

Mixing up fixed and variable cost — reading the coefficient of x as the fixed cost instead of the constant term. Also, computing average cost by dividing by the wron …