Annual salary of Arun = 7,68,000 Rs.
Monthly salary = 7,68,000/12 = Rs. 64,000
Spending on children = Rs. 12,000
Rest = 52,000
1/13th of the rest = 52,000/13 = Rs. 4,000 is spent on food.
Rs. 8,000 is spent in mutual funds.
Monthly savings = 64,000 - (12,000+4,000+8,000) = Rs. 40,000.