458) 90 * (a - 8) + 40 = 490

Решение:

1. \( 90 \cdot (a - 8) + 40 = 490 \)
2. \( 90 \cdot (a - 8) = 490 - 40 \)
3. \( 90 \cdot (a - 8) = 450 \)
4. \( a - 8 = \frac{450}{90} \)
5. \( a - 8 = 5 \)
6. \( a = 5 + 8 \)
7. \( a = 13 \)

Ответ: a = 13.