Question

(3891-Х) +25419=27090

Answer 1

3891-x+25419=27090
29310-x=27090
-x=27090-39310
x=2220

Answer 2

$3891 - x = 27090 - 25419 \ 3891 - x = 1671 \ x = 3891 - 1671$
$x = 2220$
Проверка:
(3891-2220)+25419=27090
27090=27090