Digits can be 0-9.  Each digit has 9 choices.
Letters have 26 choices.
Because digits and letters can repeat it's
26*26*9*9*9=492,804 different license plates.
If you need help understanding math so you can solve these problems yourself, then one on one online tutoring is the answer ($30/hr).  If you need faster solutions with guaranteed detailed answers, then go with personal problem solving ($3.50-$5.50 per problem).  Contact me at fcabanski@hotmail.com