Answer:
15 inches.
Explanation:
Since we know its a square, we know that the side lengths are all equal. Knowing this, we know that we could find the area by taking a side length and squaring it. So we can take the square root of 219 to find the side length:
√219 = 14.79864859 ≈ 15
Therefore, the side lengths of the sign are about 15 inches.