15m + 30 - 12m = 42
3m = 42 - 30
3m = 12
m = 4
Проверка
15 * 4 + 30 - 12 * 4 = 42
60 + 30 - 48 = 42
90 - 48 = 42
42 = 42
--------------------------------------
2*k - 391 = 73*5 + 108
2k = 391 + 365 + 108
2k = 864
k = 432
Проверка
2 * 432 - 391 = 73 * 5 + 108
864 - 391 = 365 + 108
473 = 473