Cuz

Parker just showed me all his math enrichment stuff he's done all year.  One of them was pretty funny...

It said to figure out the house number for an address of Johnny.
ABC were the numbers.
A+B+C = 4.
A was odd
B was even
C was a number you said when you count by 3.

Then he had to explain why he put down 103 as the answer.

His was: Because it was the only possibility.

This was a common theme when answered the "explain your work" question.