ok, the first digit can be any digit except 6. so there are 9 possibilities for the first digit.
For the second and third digit, you can have any number from 0 to 9, so that 10 possibilities.
the last digit has to be odd, so you can only choose from 1, 3, 5, 7, and 9. thats possibilities for the last digit.
Thus, there are 9 x 10 x 10 x 5 = 4500 different codes available.