I want to send a letter to Korea. How many stamps do I need to put on the envelope?

For a letter sent to Korea, the postage is 5.50 yuan for a letter under 20 grams. You can put a stamp of 5.50 yuan on the upper right corner or the back of the envelope. If you send a postcard, it is 4.50 yuan. Write your address (Korean or English) on the lower right of the envelope, and write your address (English; But only the other party can understand it when writing in Chinese, but if it is written in Chinese, add China PA at the bottom.