To find the sales tax charged on a purchase of $400 with a sales tax rate of 9%, you can use the following formula:
\[ \text{Sales Tax} = \text{Purchase Amount} \times \text{Sales Tax Rate} \]
Substituting the given values:
\[ \text{Sales Tax} = 400 \times 0.09 = 36 \]
So, the sales tax charged on the purchase is $36.
Next, to find the total cost of the purchase, you add the sales tax to the original purchase amount:
\[ \text{Total Cost} = \text{Purchase Amount} + \text{Sales Tax} \]
Substituting the values:
\[ \text{Total Cost} = 400 + 36 = 436 \]
Therefore, the total cost of the purchase, including sales tax, is $436.