Solution: Suppose the original plan is x kilometers per hour, and the actual average speed is 0.5x kilometers per hour.

Because 9 minutes =0. 15 hours.

16/x+0. 15 = 16/0.5x。

Multiply both sides by 0.5x, so.

8+0.075x= 16

Get x=320/3.

Test: When x=320/3, 0.5x is not equal to 0.

X=320/3 is the solution of the original equation.

A: The original planned speed is 320/3 kilometers per hour.