Give the step-by-step reasoning process and then the final answer. At the park, Dimitri saw families riding bicycles and tricycles. Bicycles have two wheels and tricycles have three wheels. 6 adults were riding bicycles and 15 children were riding tricycles.  How many wheels did Dimitri see at the park?
Dimitri saw 2 x 6 = 12 wheels on the bicycles. He saw 15 x 3 = 45 wheels on the tricycles. He saw a total of 12 + 45 = 57 wheels.
The final answer: 57.