Answer:
The correct answer is B. 18 inches.
Step-by-step explanation:
Let's recall that Yield signs are shaped like downward-pointing triangles (as you can see in the picture below) and the formula for finding the Area of a triangle is:
Area = (Base * Height) /2
Replacing with the real values we have:
108 = (Base * 12)/2
216 = 12 * Base
Base = 216/12
Base = 18 inches
The top edge of the sign is 18 inches length.