158+262+138
=158+(262+138)
=158+400
=558

375+219+381+225
=(375+225)+(219+381)
=600+600
=1200

-232
=5001-(247+1021+232)
=5001-1500
=3501

(181+2564)+2719
=(181+2719)+2564
=2900+2564
=5464