To calculate the sales tax on the shirt, you can use the following formula:
\[ \text{Sales Tax} = \text{Price of the Shirt} \times \text{Sales Tax Rate} \]
In this case, the shirt costs $20 and the sales tax rate is 7% (or 0.07 as a decimal):
\[ \text{Sales Tax} = 20 \times 0.07 = 1.40 \]
Now, to find the total cost of the shirt after tax, you add the sales tax to the original price of the shirt:
\[ \text{Total Cost} = \text{Price of the Shirt} + \text{Sales Tax} = 20 + 1.40 = 21.40 \]
So, the sales tax is $1.40, and the cost of the shirt after tax is $21.40.
The correct response is: Sales tax = $1.40; Cost of shirt after tax = $21.40.