3.78+（6.22+4.72）
=3.78+6.22+4.72
=10+4.72
=14.72
18.73+3.85-2.73
=18.73-2.73+3.85
=16+3.85
=19.85
45.6-（83.7-78.8）
=45.6-4.9
=45.6-5+0.1
=40.6+0.1
=40.7