(х+408)-312=501
х+408=501+312
х+408=813
х=813-408
х=405
(405+408)-312=501
813=312=501
501=501
x + 408 = 312 + 501
x = 312 + 501 - 408
x = 405
(х+408)-312=501
х+408=501+312
х+408=813
х=813-408
х=405
(405+408)-312=501
813=312=501
501=501
x + 408 = 312 + 501
x = 312 + 501 - 408
x = 405