To convert 34m29cm to dm, we need to convert meters to decimeters and add the centimeters.

1 meter = 10 decimeters
1 centimeter = 0.1 decimeters

34 meters = 34 * 10 = 340 decimeters
29 centimeters = 29 * 0.1 = 2.9 decimeters

Total = 340 decimeters + 2.9 decimeters = 342.9 dm

Therefore, 34m29cm is equal to 342.9 dm.