Xiaowen travels 6 kilometers per hour from A to B, 9 kilometers per hour when he comes back, and 5 hours back and forth. How many kilometers did Xiaowen walk back and forth?

Suppose: the time to go is X.

Because the round trip distance is equal.

There is 6x=9(5-x)

The solution is x=3.

So the distance is 3*6= 18km.

* * * Disappeared 18*2=36(6*3+9*(5-3))