Your task is to write a method `countSevens`

that counts the number of digits equal to 7 in a given number. For example,
the call `countSevens(1797)`

should return 2 since the number
contains two digits 7.

Hint: Repeatedly compute `% 10`

and
`/ 10`

.

Complete the following code:

public class Numbers { /** Counts the number of digits with value 7 in a given number @param n any non-negative number @return the number of digits with value 7 in the decimal representation of n */ public int countSevens(int n) { // your work here } }