because there are 12 in one layer and there are 3 layers
By scientific notation I am assuming you mean standard form, as that is used primarily in scientific calculations. The answer in standard form would be

I hope this helps!
Answer: 2 bookcases.
Step-by-step explanation:
Let be "x" the number of bookcases that the custodian will be able to repaint completly with 5 gallons of paint.
According to the data given, the custodian needs 2 gallons of paint to repaint one bookcase. Since all the bookcases are equal, you can set up the following proportion:

Now you must solve for "x" in order to find its value:

Notice that the custodian will be able to repaint 2 bookcases completely, then you can say that:

<span>A. 45:6 = 15:2
B. 54:36 = 3:2
C. 12:8:16 = 3:2:4</span>