The original price would be 100%
A 21% discount means the shirt is on sale for 100% -21% = 79% of the original price.
Divide 79% by 100 to get a decimal:
79/100 = 0.79
Multiply the original price by 0.79 to get the discounted price:
20 x 0.79 = 15.80
The new price is $15.80
