To find the sales tax rate, we can use the formula:
\[ \text{Sales Tax Rate} = \frac{\text{Sales Tax}}{\text{Cost before Tax}} \times 100 \]
In this case:
- Sales Tax = $23.40
- Cost before Tax = $390
Now, substitute the values into the formula:
\[ \text{Sales Tax Rate} = \frac{23.40}{390} \times 100 \]
Calculating the fraction:
\[ \text{Sales Tax Rate} = 0.06 \times 100 \]
Now, calculate the percentage:
\[ \text{Sales Tax Rate} = 6% \]
Thus, the sales tax rate is 6%.