Unit digit can be chose in 2 ways- either 0 or 5.
When unit digit is 5:
With just a single 6:
Number of numbers possible = 5 * 5 * 4 = 100 (as MSD cannot be a 0)
Now, two 6's can come as 66x 6x6 or x66, and this counts to 5 + 5 + 4 = 14 numbers (for the last case, x can only be from 1-4 and not 0)
So, total numbers ending in 5 = 100 + 14 = 114.
When unit digit is 0:
With just a single 6:
Number of numbers possible = 6 * 5 * 4 = 120
Now, two 6's can come as 66x 6x6 or x66, and this counts to 5 + 5 + 5 = 15 numbers.
So, total numbers ending in 0 = 120 + 15 = 135.
Thus, total numbers divisible by 6 = 114 + 135 = 249.