Here's how to convert the diameter of Earth from kilometers to decimeters:

1. Convert kilometers to meters:

* There are 1000 meters in 1 kilometer.

* So, 1.3 x 10^4 km = 1.3 x 10^4 * 1000 m = 1.3 x 10^7 m

2. Convert meters to decimeters:

* There are 10 decimeters in 1 meter.

* So, 1.3 x 10^7 m = 1.3 x 10^7 * 10 dm = 1.3 x 10^8 dm

Therefore, the diameter of Earth is 1.3 x 10^8 decimeters.