Explanation

Since he spent 88% of his income, he has 12% of his income left (100% - 88% = 12%).

We know that 12% of his income is Rs. 2160, so we can set up the equation:

12% of x = 2160

To solve for x, we can convert the percentage to a decimal by dividing by 100:

0.12x = 2160

Now, divide both sides by 0.12:

x = 2160 / 0.12

x = 18000

So, his income is Rs. 18000!