A number is divisible by 3 if, and only if the sum of its digits is divisible by 3 is already divisible by 3 since .
To make divisible by 3, X itself must be divisible by 3.
So to make 35X64 divisible by 3, X itself must be divisible by 3, or zero.
The possible values for X are
0, 3, 6, and 9.