$$\frac{20}{49}:\frac{15}{63}=$$

$$\frac{20}{49}\times\frac{63}{15}=$$

$$\frac{\cancelto{4}{20}}{\cancelto{3}{15}}\times\frac{\cancelto{9}{63}}{\cancelto{7}{49}}=$$

$$\frac{4}{3}\times\frac{9}{7}=$$

$$\frac{4}{\cancelto{1}{3}}\times\frac{\cancelto{3}{9}}{7}=$$

$$\frac{12}{7}$$