## Precalculus (6th Edition) Blitzer

$144$ numbers
It is an odd number; the last digit can only be $7, 9$ (2 choices). The number is less than 6000, so the first digit can only be $2,4$ (2 choices). Assume the digits can be used repeatedly. The middle two digits have $6$ choices each, so the total number of ways is $2\times6\times6\times2=144$