解：设四月份用电x度，电费0.5x元。根据题意，得0.43*140+0.57（x-140）=0.5x                                 60.2+0.57x-79.8 =0.5x                                          0.57x -19.6= 0.5x                                                   0.07x=19.6                                                          x=280                                              0.5*280=140（元）答：四月份用电280度，应交电费140元。

这个是什么意思呢？问题呢？