Whenever a number is followed by percent, you can turn it into a fraction by simply moving the decimal places two places to the left:
90.0 % becomes .90
As a fraction, this is 90 over 100. To reduce it to its simplest form, divide by 10:
9/10
Check the picture below. Recall, is an open-top box, so, the top is not part of the surface area, of the 300 cm². Also, recall, the base is a square, thus, length = width = x.

so.. that'd be the V(x) for such box, now, where is the maximum point at?

now, let's check if it's a maximum point at 10, by doing a first-derivative test on it. Check the second picture below.
so, the volume will then be at
Answer:
d.
Step-by-step explanation: