h(n) represents hash n. Assuming the long number represents n=16000811607, then we need h(16000811607). 625=252=(100/4)2. Any number ending in 4 zeroes is a multiple of 625. This means that we only need to inspect the last four digits of n, which are 1607.
10000=5000×2=2500×4=1250×8=625×16.
1607=1250+357, so h(n)=357. This is another way of saying 1607 when divided by 625 leaves a remainder of 357=n mod 625.
Another possible interpretation is to take the two 5-digit numbers and perform some operation between them and let n be the result of this operation. For example, n=81160-16000=65160.
So 5160 is the 4-digit number. 5160-5000=160, so h(n)=160.
The leading 0 and final 7 may have nothing to do with calculating the hash, representing something else in the business or commercial organisation.