Answer:
750 license plates meet this description.
Explanation:
We have to find all possible 4-digit numbers that start with 3, 6 or 8 and the other 3 digits are odd. The digits can be repeated.
For the first digit we have 3 options (3,6,8) and for the other digits we have 5 options (1,3,5,7,9).
Therefore, the total of options we have are 3x5x5x5 = 375 different numbers with this characteristics.
Finally we can pair these numbers with HG or YG, therefore we have to multiply this number by two. 375 x 2 = 750.
So we can conclude that 750 plates meet this description.