(х + 312) * 2 = 1000
х + 312 = 1000: 2
х + 312 = 500
х = 500 — 312
х = 188
(х — 312) * 2 = 1000
х — 312 = 1000: 2
х — 312 = 500
х = 500 + 312
х = 812