The numbers of three digit number can be formed by using the digits 0, 1, 2, 3, 7, 9 if any digit can be used in any number of time, is

Consider the 3 digit number as
- - -
The total number of digits available are $0,1,2,3,7,9$.
Hence the number of ways in which we can fill the first place will be
$6-1$
$=5$ ...(excluding 0).
Similarly the second place can be filled in $6$ ways.
The third place can be filled in $6$ ways.
Hence in total there will be
$5\times 6\times 6$ numbers
$=36\times 5$

$=180$.