To find the cost of the extended warranty, you can calculate 18% of the purchase price of the ceiling fan, which is $140.
First, convert the percentage to a decimal:
\[ 18% = \frac{18}{100} = 0.18 \]
Next, multiply the purchase price by the decimal:
\[ \text{Warranty cost} = 0.18 \times 140 \]
Calculating that:
\[ \text{Warranty cost} = 25.2 \]
Therefore, the cost of the extended warranty is $25.20.
The correct answer is b. $25.20.