Correct Answer - Option 1 : Rs. 10000

**Given **

Remaining amount after all expenses = Rs. 3900

**Formula Used **

Percentage = (Actual/Total) × 100

**Calculation **

**Let the monthly salary of himanshu be 100x **

Himanshu spend on clothes = 20% of 100x = 20x

On food = 15% of 100x = 15x

Remaining = 100x - (20x + 15x) = 65x

Spend on rent = 40% of 65x = 26x

so, total expenses of Himanshu = 35x + 26x = 61x

Remaining amount after all expenses = 3900

⇒ 100x - 61x = 3900

⇒ x = 100

⇒ 100x = 10000

**∴ The Himanshu earned in the month is Rs. 10000**