Hint
Something's wrong with the letter O, and the word 'oifoeront' is important to the answer.
Answer
15 different letters: acdefhilmrstvwy.
Reasoning
The sentences should read:
As you can see, my printer replaces every third letter with the letter 'o'.
How many different letters have been replaced?
??
Puzzle 3
Below is a grid which should contain animals. The missing letters for a particular column are listed at the top of that column. Can you 'drop' the missing letters in and complete the grid? Each animal begins with a different letter of the alphabet.