分数四则运算100题，还有答案，不超过4步

1.3/7 × 49/9 - 4/3 =1 2.8/9 × 15/36 + 1/27 =11/27 3.12× 5/6 ? 2/9 ×3 =28/3 4.8× 5/4 + 1/4 =41/4 5.6÷ 3/8 ? 3/8 ÷6 =255/16 6.4/7 × 5/9 + 3/7 × 5/9 =5/9 7.5/2 -（ 3