To evaluate the common logarithm of a number can be seen as finding what exponent the number 10 must be raised to in order to get that number. Here, we take the logarithm of the number 102. We already know that we raise 10 to 2 to get that number. Therefore, we can evaluate the logarithm immediately.
What exponent do we raise 10 to the power of in order to get 0.001? We need to write 0.001 as a power of ten. We start by writing it as a fraction, which we then can rewrite to a power of ten.