If the length of the wall is 18 feet, then the wall on the plan is 3.6 inches long
Solution:
According to Tom, 2.6 inches equals to 13 feet
Length of the wall = 18 feet
If 2.6 inches is equal to 13 feet, then 1 feet is equal to:

So, 1 feet = 0.2 inches …….(1)
Now, we have to determine the length of the wall on the plan which is 18 feet long
Using Equation (1), 18 feet = 18 × 0.2 inches = 3.6 inches
Hence , the wall on the plan is 3.6 inches long