13 disc-shaped objects (height 12/13 cm) are to be stacked

It is a cylinder inserted in a rectangular box.

Dimension of the rectangular box:
l=5
w=5
h=13*(12/13)=12
Total Volume = l*b*h = 25*12

Dimension of the inserted cylinder:
r = (5/2). Please see the attached image providing a top view of the box. As the lateral edges of the box touch the circle and appear as tangent to the circle. The length and width of the rectangle become equal to diameter of the circle.

h = 13*(12/13)=12
Volume occupied \(\pi*r^2*h = \frac{22}{7}*(\frac{5}{2})^2*12= \frac{22}{7}*\frac{25}{4}*12\)

Volume left for the gel = Total Volume of the box - Volume occupied by cylinder

\(25*12 - \frac{22}{7}*\frac{25}{4}*12 = 25*12(1-\frac{22}{28})\)

\(25*12*\frac{6}{28}=\frac{450}{7}=64.2 \approx 65\)

Ans: "B"