х * 8 = 720
х = 720 : 8
х = 90
проверка:
90 * 8 = 720
720 = 720
...................................................................................................
420 - у = 210
420 - 210 = у
у = 210
проверка:
420 - 210 = 210
210 = 210
...........................................................................................................
240 : а = 4
а = 240 : 4
а = 60
проверка:
240 : 60 = 4
4 = 4
.....................................................................................................................
с + 356 = 900
с = 900 - 356
с = 544
проверка:
544 + 356 = 900
900 = 900