To find the total cost \( y \) for buying \( x \) shirts, we know that Nicholas has a cost of \( 9.50 \) for each shirt and a one-time fee of \( 22.50 \) for the design.
The equation can be represented as follows:
The cost for the shirts is \( 9.50 \) multiplied by the number of shirts \( x \), and the one-time design fee is added to that cost.
So the correct equation is:
\[ y = 9.50x + 22.50 \]
Thus, the correct answer is A. \( y = 9.50x + 22.50 \).