Martha has 19 butterflies in her collection. She has twice as many blue butterflies as yellow butterflies. The rest of her butterflies are black. If Martha has 6 blue butterflies, how many black butterflies does she have?
Martha has 6/2=<T>divide(6, 2)=3.0 yellow butterflies.
Martha has 6+3=<T>add(6, 3)=9 blue and yellow butterflies.
Martha has 19-9=<T>subtract(19, 9)=10 black butterflies.
