458) 90 × (a - 8) + 40 = 490
Решим уравнение:
90 × (a - 8) + 40 = 490
90 × (a - 8) = 490 - 40
90 × (a - 8) = 450
a - 8 = 450 : 90
a - 8 = 5
a = 5 + 8
a = 13
Ответ: a = 13