13a.) If you're dividing and the base (in this case the base is 10) is the same, subtract the exponents.
13b.) If you're multiplying and the base is the same, then you add the exponents:
13c.) This is similar to 13b:
13b.) If you're multiplying and the base is the same, then you add the exponents:
13c.) This is similar to 13b: