Answer: $9.81
Explanation:
Here, Tiffany buys a basket of watermelons on sale for $9 before tax.
Therefore, Initial cost of a basket of watermelons = $9
And, he sales tax is 9%.
Therefore tax on a basket of watermelons,
9% of 9 =

But, The total cost of a basket of watermelons = initial cost + tax
= 9+0.81=9.81
Therefore, Tiffany pays $9.81 for the basket of watermelons.