Working 8 hours a day, Ashu can copy a book in 18 days.
Question:

Working 8 hours a day, Ashu can copy a book in 18 days. How many hours a day should he work so as to finish the work in 12 days?

Solution:

If Ashu works for 8 hours daily, he can finish the work in 18 days.

If he works for 1 hour daily, he can finish the work in $(18 \times 8)$ days or 144 days.

$\therefore$ Number of hours he should work daily to finish the work in 12 days $=\frac{144}{12}=12$