A man completes a work in 15 days by working 4 h per day for 5 days, 5 h per day for 5 days and 6 h per day for 5 days. If he works 8 h per day with half an hour lunch break, he will complete the work in:

Correct option is A

Given:
A man completes work in 15 days by working 4 h per day for 5 days, 5 h per day for 5 days, and 6 h per day for 5 days.
Formula Used:
​$$M_1 × D_1 × H_1 = M_2 × D_2× H_2$$​​
where $$M_1$$​ and $$M_2$$​ are numbers of men, $$D_1$$​ and $$D_2$$​ are the numbers of days, $$H_1$$​and $$H_2$$​ are numbers of hours.
we can only use the term given in the question.
Solution:
Let the efficiency of 1 man be 1 unit
According to the question.
Total work = 5 × 4 + 5 × 5 + 5 ×6
Total work = 75 units
After an hour break = 8 hours - 30 minutes
=> After an hour break = 7 hours 30 minutes.
Now, Total work = 7.5 × no of days
=> 75 = 7.5 × D
=> D = 10 days