Here's a tool for your math toolbox:
Wherever you see the word "per", it wants division.
You should begin with a fraction.
"People per square kilometer"
means
(number of people) / (number of square kilometers) .
The problem just gave you both of those numbers. So it's time to
polish up your pencil or your calculator and get to work dividing.
Notice that you made a mistake copying the estimated population
of China, and then, even worse than that, you didn't proofread your
question and correct the copying mistake.
(Population) / (area) =
(1,313,973,713 people) / (5,956,960 sq km) =
220.6 people per square km.
