Definition: The logarithm of a number, to a particular base, is the power to which the base must be raised to give the given number.
So, let log2 (64) = x, where the base of the logarithm is 2.
Going by the above definition, log2 (64) is x, so 64 (the given number) must be 2 (the base) to the power x.
i.e. 64 = 2^x
but 64 = 2^6
i.e. 2^6 = 2^x
Therefore, x = 6
Answer: log2 (64) = 6