Ответ:\(\frac{12}{18}=\frac{12\div6}{18\div6}=\frac23\).\(\frac6{54}=\frac{6\div6}{54\div6}=\frac19\).\(\frac{56}{98}=\frac{56\div14}{98\div14}=\frac47\).\(\frac{42\cdot24}{8\cdot21}=\frac{42}{21}\cdot\frac{24}{8}=2\cdot3=6\).