Explanation:

To solve this question, we can apply a short trick approach;
If M₁ persons can do a piece of work in D₁ days working H₁ hours a day and M₂ persons can do the same work in D₂ days working H₂ a day then we have a short-trick formula which is M₁D₁H₁ = M₂D₂H₂
Given:
M₁ = 50, D₁ = 12 days, H₁ = 6 hours/day
M₂ = 60, D₂ = 8 days, H₂ = ?
Now, as
M₁D₁H₁ = M₂D₂H₂
50 × 12 × 6 = 60 × 8 × ?
⇒ ? = 50 × 12 × 6 / 60 x 8 = 60/8
= 15/2 = 7 1/2 hours