Basically you need to understand the logic for this problem.
1 byte = 8 bit  ( Are sure you dont mean 8 bits, bit and byte are different)
You can find the largest possible integer value possible with any bit with this forlula: (2^n-1)
In your case  Total integer = 2^64 = 18446744073709551616
That means you can represent 0 to 18446744073709551615 with 8 bytes.

#include<math.h> main() { double b = 64; b = pow(2,b); }

This is not a complete code, try for yourself. If you still have doubt contact me