Final answer:
When the scale of a drawing is described as 15:20, the length of a wall in the actual building can be found by setting up a proportion.
Step-by-step explanation:
When the scale of a drawing is described as 15:20, it means that for every 15 units on the drawing, there are 20 units in the actual building. To find the length of the wall in the actual building, we can set up a proportion:
15 units (drawing) / 20 units (actual) = 10 inches (drawing) / x inches (actual)
By solving this proportion, we find that the length of the wall in the actual building is 20 inches. Therefore, the correct answer is 20 inches.