To solve the equation \(2.5x = 30\), we can find \(x\) by dividing both sides by 2.5:
\[ x = \frac{30}{2.5} = 12 \]
This means that \(x = 12\), indicating that Niall can make 12 cards with 30 inches of ribbon.
Therefore, the correct interpretation of the solution is 12 cards.