How many 3's on the phone eye test?

The answers for 'eye test how many 3's puzzle ranges from 15 to 21. At first glance, most people only notice 15 threes in the image. First, you might notice that there are two threes on the number pad, as the number eight has also been replaced by a three. Then there are eight threes in the phone number.

i think that the correct answer is

c. p equals 5,000 times, 0.3, to the power of the fraction m over 20