The expression 62.4d-21062.4d-210 gives the number of Indian rupees you receive when you exchange / $d$d at the local currency exchange.

How many Indian rupees do you receive when you exchange / $13$13?

It is very easy, you'll see. Let's suppose that x is the value or result, so x=62.4 (d) - 210, from where you must replace d = 13 (is given in the exercise). So if you want to know how many Indian rupees you receive, operate the equation:

x = 62.4 * (13) - 210

x = 811.2 - 210

x = 601.2.

In consequence, the quantity you receive is 601.2 Indian rupees.