In one of the problems in Schweser, the operating expenses are assumed to be 30% fixed and 70% variable. If 100k sq ft was fully occupied, the utility expense would be $6/sq ft. The problem asks :what is the utility expense per occupied sq ft if the building is 90% occupied?

This is what I did.

If 100k sq qas fully occupied, we would have total operating expense of 600,000$ where 180,000$ are fixed ( 1.8$ per sq ft) and 420,000$ are variable ( 4.2$ per sq ft)

Now 90% is occupied, so the fixed costs would remain the same, meaning180,000$ and the variable costs would be 378,0000$ which makes sense because occupancy is low and operating expense is supposed to be lower ,but I am not sure why the book goes futher and does 558,000/90,000 to get 6.20$ .

I stopped at 5.58$ thinking that was the answer, why did the costs go up to 6.20?

Please help me