Notez numarul cu a
( a × 5 + 9 999 ) × 6 + 18 000 920 = 87 000 374
( a × 5 + 9 999 ) × 6 = 87 000 374 - 18 000 920
( a × 5 + 9 999 ) × 6 = 68 999 454
a × 5 + 9 999 = 68 999 454 : 6
a × 5 + 9 999 = 11 499 909
a × 5 = 11 499 909 - 9 999
a × 5 = 11 489 910
a = 11 489 910 : 5
a = 2 297 982 → numarul