(3/8+4/7)×56 =3/8×56+4/7×56 =21+32 =53
原式=56x(3/7 -3/8 +9/14)=56x3/7 -56x3/8 +56x9/14=8x3-7x3+4x9=24-21+36=3+36=39
56x(3/7-3/8+9/14)=56x3/7-56x3/8+56x9/14=24-21+36=39