1001 claims

If we multiply an $n$ digit number $a$ by $10^n$ , we get $n$ zeros to the right of that number. When we add that number with the product, we get a number of the form $\overline {aa}$ . So, by multiplying an $n$ digit number $a$ with $10^n+1$ , we get the number $\overline {aa}$ . In this example, by multiplying $715$ with $1001$ we get $715715$ .

Since '715' is the friend's answer - we will assume that 715 is the number.

So $715 * 1001$ = $715 * 1000$ + $715 * 1$ = $715715$ . Therefore (715715, 'cause he is first multiplying by 1000 and then by one and adding it together.) is the answer.

Well it was easy what you have to do it just muplitpy 1001 times 715 or do the divsion way 715715 divdie by 715