9/20÷(1/3-1/5)×9/14
=9/20÷(5/15-3/15)×9/14
=9/20×15/2×9/14
=(9×15×9)/(20×2×14) (这一步可约分,上下各除以5）
=(9×3×9)/(4×2×14)
=243/112