The destination code for Beijing is "PEK" and Shanghai is "PVG." The next slot is "Return advanced routing code," which needs the same code you placed in the first "advanced routing code" slot.
The last thing you'll need to do is choose "See calendar of lowest fares" and enter "3-10" for the length of stay if you're headed out of Seattle or "9-16" for Phoenix or Dallas.
Then you'll find a calendar like the one above that can help you get out of town because taking a vacation now is worth it. Don't wait until next year. Make it happen now. Though, if you want these prices, get on it soon. Prices change quickly and these could be gone soon.
h/t The Flight Deal
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