计算，能简算的要简算．
①6.21﹣3.8+2.2                   ②6.03+3.7+2.97
③17.43﹣6.57﹣2.43               ④20.47﹣（1.47+6.8）
⑤13.26+4.71+3.47+5.29            ⑥22.74+8.68﹣13.74．