Answer:
The shirt would cost you $14.40 after the 20% sale.
Explanation:
What you would need to do is multiply 18 by .20, to get 3.6, this is how much money is taken off the cost.
Once you have done this, subtract 3.6 from 18.
18-3.6
This will then get you your cost of $14.40
Hope this helps!