怎样简便怎样算．
7.28﹣（0.8+3.28）          3.15+1.83+6.85+2.17           13.86﹣2.99
13.92﹣（3.92﹣2.74）       2.72﹣3.98+5.28﹣2.02         0.27﹣4.9+4.83+2.9．