First, we need to find the discount. 10% of $20 is computed as follows:
[tex]20\text{ \$}\cdot\frac{10}{100}=2\text{ \$}[/tex]Applying the discount, the price is $20 - $2 = $18
In taxes, you have to pay 1.5% of the cost, that is,
[tex]18\text{ \$}\cdot\frac{1.5}{100}=0.27\text{ \$}[/tex]Therefore, the total cost is $18 + $0.27 = $18.27