Решим каждое уравнение по отдельности:
-
$$18n - 12n - 3n = 186$$
$$3n = 186$$
$$n = 186 : 3$$
$$n = 62$$
-
$$25a - 7a - 8a = 400$$
$$10a = 400$$
$$a = 400 : 10$$
$$a = 40$$
-
$$2x + 8x - x = 243$$
$$9x = 243$$
$$x = 243 : 9$$
$$x = 27$$
-
$$6y - y + 4y = 234$$
$$9y = 234$$
$$y = 234 : 9$$
$$y = 26$$
Ответ: 1) n = 62; 2) a = 40; 3) x = 27; 4) y = 26