Answer:The sales tax rate is 5.45%.
Explanation:
Let X be the percent sales tax rate.
The cost of the sales tax is $21.09 - $20 = $1.09.
The cost of the sales tax is X% of the original price, or X/100 * $20 = $1.09.
Dividing both sides by $20 and multiplying by 100% gives:
X = 1.09 / 20 * 100% = 5.45%.
The sales tax rate is 5.45%.