Start by considering that a decimeter is one tenth of a meter. That's 1/10th of a meter. Not very much. How many miles are in a tenth of a meter. Only a small fraction. It turns out that 0.1 meters equals about 6.2137 × 10-5 miles, or 0.000062137 miles. Your 350 decimeters is 0.0217479917 miles. There are about 1609.344 metres in a mile, so you'll make your calculation from there.