Задание

\dfrac{2}{3}\cdot 12=\dfrac{2}{3}\cdot \dfrac{12}{1}=\dfrac{2\cdot \overset{\tiny{4}}{\cancel{12}}}{\underset{\tiny{1}}{\cancel{3}\cdot 1}}=\dfrac{2\cdot 4}{1\cdot 1}=\dfrac{8}{1}=8

\dfrac{2}{3}\cdot 15=\dfrac{2}{3}\cdot \dfrac{15}{1}=\dfrac{2\cdot \overset{\tiny{5}}{\bcancel{15}}}{\underset{\tiny{1}}{\bcancel{3}\cdot 1}}=\dfrac{2\cdot 5}{1\cdot 1}=\dfrac{10}{1}=10