Ответы и объяснения

2013-12-04T16:28:45+04:00

1300-(b+800)=400                                                                                                                (b+800)=1300-400                                                                                                                (b+800)=900                                                                                                                          b=900-800                                                                                                                             b=100                                                                                                                                    1300-(100+800)=400                                                                                                             400=400