Calculate the Cost of Goods Sold (COGS) and the profit given sales of 100,000 FCFA and COGS is 80% of sales. Then, calculate the margin rate.

The Cost of Goods Sold is 80% of the sales.

$$\text{COGS} = 0.80 \times \text{Sales}$$ $$\text{COGS} = 0.80 \times 100,000 \text{ FCFA}$$ $$\text{COGS} = 80,000 \text{ FCFA}$$

Profit is calculated as Sales minus Cost of Goods Sold.

$$\text{Profit} = \text{Sales} - \text{COGS}$$ $$\text{Profit} = 100,000 \text{ FCFA} - 80,000 \text{ FCFA}$$ $$\text{Profit} = 20,000 \text{ FCFA}$$

The correct option is B.
The amount of profit is $\boxed{\text{B. 20,000 FCFA}}$.

The margin rate (or gross profit margin) is calculated as Profit divided by Sales, expressed as a percentage.

$$\text{Margin Rate} = \frac{\text{Profit}}{\text{Sales}} \times 100\%$$

Using the profit from Question 39:

$$\text{Margin Rate} = \frac{20,000 \text{ FCFA}}{100,000 \text{ FCFA}} \times 100\%$$ $$\text{Margin Rate} = 0.20 \times 100\%$$ $$\text{Margin Rate} = 20\%$$

The correct option is B.
The margin rate is $\boxed{\text{B. 20\%}}$.