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 = <T>multiply(2, 6)=12 wheels on the bicycles.
He saw 15 x 3 = <T>multiply(15, 3)=45 wheels on the tricycles.
He saw a total of 12 + 45 = <T>add(12, 45)=57 wheels.
