Hi,
1)You are ignoring the vacant space between cylinders. So, you cannot get the number by dividing areas.
2)We need to know the dimensions of the box in order to calculated the number of cylinders that can be fit.
For example:
if the diameter of circle is 4 units and the area is 100 units
If the dimensions of box is 25x4, 25 cylinders will fit.
If the dimensions of box is 10x10, only 20 cylinders will fit.

It's easiest to think in extremes for this type of problem since no integer constraints are given.

1) The length and width of the box are not given. The box could be a mile wide or 2cm wide. Insufficient.

2) The size of the candies is not given. Their diameter could be 10 centimeters or 10 miles. Insufficient.

Combined) With a square base, the box would be 10 x 10 and could fit some quantity of candies. With a length of 0.00001, not even one candy would fit into the package. Insufficient.

FYI: if you wanted to calculate the number of candies that would fit into a square base, it would go as follows:

C = 2*pi*r = 2, so r = 1/pi and d = 2/pi

We could partition the box into 10 /(2/pi) = 5pi, or 15 rows (rounding down to nearest integer from ~15.7) and 15 columns. The number of partitions and thus candies would be 15 * 15 = 225.