We know that $\text{AFC} = \frac{\text{TFC}}{Q}$. Given that AFC at 4 units is Rs 5, we have $\text{TFC} = \text{AFC} \times Q = 5 \times 4 = 20$. Since total fixed cost remains constant at all output levels, $\text{TFC} = 20$ for every quantity.

Total variable cost is $\text{TVC} = \text{TC} - \text{TFC}$. For each output level, we subtract 20 from the given TC. Average variable cost is $\text{AVC} = \frac{\text{TVC}}{Q}$, average fixed cost is $\text{AFC} = \frac{\text{TFC}}{Q} = \frac{20}{Q}$, and short-run average cost (also called SAC) is $\text{SAC} = \frac{\text{TC}}{Q}$. Short-run marginal cost is $\text{SMC} = \text{TC}_n - \text{TC}_{n-1}$, the change in total cost when output increases by one unit.

Working through the calculations:

The logic of cost decomposition

Total cost splits into two components: the part that does not change with output (fixed cost, like rent or a manager's salary) and the part that does (variable cost, like raw materials and hourly wages). Mathematically,

Fixed cost is the same whether you produce one unit or six; variable cost starts at zero when output is zero and rises as production expands. Once we know $TFC$, everything else falls into place: $TVC$ is simply $TC - TFC$, average fixed cost is $AFC = \frac{TFC}{Q}$, average variable cost is $AVC = \frac{TVC}{Q}$, short-run average cost (also called $AC$ or $SAC$) is $\frac{TC}{Q}$, and short-run marginal cost is the increment in total cost when output rises by one unit, $SMC = \Delta TC / \Delta Q = TC_n - TC_{n-1}$.

The question hands us a single anchor: at $Q=4$, average fixed cost is Rs 5. That tells us

Because fixed cost never changes, $TFC = 20$ at every level of output. Now we can fill in the rest.

Step-by-step construction of the schedules

For $Q=1$:

$TVC = 50 - 20 = 30$

$AFC = \frac{20}{1} = 20$

$AVC = \frac{30}{1} = 30$

$SAC = \frac{50}{1} = 50$

$SMC$: not defined for the first unit in this table (no prior output to compare), though one could interpret it as the change from zero output; we'll compute it from $Q=2$ onward.

For $Q=2$:

$TVC = 65 - 20 = 45$

$AFC = \frac{20}{2} = 10$

$AVC = \frac{45}{2} = 22.5$

$SAC = \frac{65}{2} = 32.5$

$SMC = 65 - 50 = 15$

For $Q=3$:

$TVC = 75 - 20 = 55$

$AFC = \frac{20}{3} \approx 6.67$

$AVC = \frac{55}{3} \approx 18.33$

$SAC = \frac{75}{3} = 25$

$SMC = 75 - 65 = 10$

For $Q=4$:

$TVC = 95 - 20 = 75$

$AFC = \frac{20}{4} = 5$ (matches the given information)

$AVC = \frac{75}{4} = 18.75$

$SAC = \frac{95}{4} = 23.75$

$SMC = 95 - 75 = 20$

For $Q=5$:

$TVC = 130 - 20 = 110$

$AFC = \frac{20}{5} = 4$

$AVC = \frac{110}{5} = 22$

$SAC = \frac{130}{5} = 26$

$SMC = 130 - 95 = 35$

For $Q=6$:

$TVC = 185 - 20 = 165$

$AFC = \frac{20}{6} \approx 3.33$

$AVC = \frac{165}{6} = 27.5$

$SAC = \frac{185}{6} \approx 30.83$

$SMC = 185 - 130 = 55$

The complete cost schedules …