Given:
Marked price of t-shirt = 420
Discount rate = 20%
To find:
The price of the t-shirt after discount.
Solution:
The price of the t-shirt after discount is 20% of less than the marked price of it.
Price of the t-shirt after discount = Marked price - 20% of Marked price
=

=

=

Therefore, the price of the t-shirt after discount is P336.