Using a 1/4″ per foot scale, it is determined that the total number of scaled inches of 4″ roof drain pipe is 10-1/2″. What is the actual length of 4″ roof drain represented by the 10-1/2″ ?

Using a 1/4″ per foot scale, it is determined that the total number of scaled inches of 4″ roof drain pipe is 10-1/2″. What is the actual length of 4″ roof drain represented by the 10-1/2″ ?