According to the information given in the exercise, the bill before the tax and tip was $13.90 and the sales tax of 6% was added to that amount.
By definition, you can write 6% as a Decimal number by dividing it by 100. Then, this is:
[tex]\frac{6}{100}=0.06[/tex]Let be "t" the amount (in dollars) of the sales tax.
To find the value of "t", you can set up the following equation:
[tex]t=(13.90)(0.06)[/tex]Finally, evaluating, you get that this is:
[tex]t=0.834[/tex]Rounded to the nearest cent, this is:
[tex]t\approx0.83[/tex]The answer is: $0.83
