1)3*1=3(уч.)-за тремя партами                                                                                                      2)17-3=14(п.)-осталось                                                                                                                  3)14*2=28(уч.)-за 14 партами                                                                                                        4)28+3=31(уч.)-в классе                                                                                                  ответ в классе 31 ученик