A building has gross area of 345,884 sf. The rentable square feet, after subtracting the space for the vertical penetrations (elevator shaft, stairwells) and mechanical rooms, totals 329,890sf. The total usable square feet is 303,550sf.

What is the "loss factor" for the building?

a. 1.087

b. 8.68%

c. 1.139

d. 7.99%

e. 13.95%