Athree-dimensional model of lucia’s apartment is shown. to cool the whole apartment, an air conditioner must provide 2.5 btus per cubic foot.

how many btus are needed to cool lucia’s apartment?

19,600 btus

19,800 btus

20,400 btus

24,000 btus

The first thing you should do is look for the volume of the apartment which in this case will be given by:
 V = ((20 * 12) + ((20-9) * 16) + (20 * 20)) * (10) = 8160 ft ^ 3
 an air conditioner must provide 2.5 BTUs per cubic foot
 So
 2.5 * (8160) = 20400 BTU.
 The correct answer is 20400 BTU.