Answer:
Dimension of the box is 
The volume of the box is 280.05 in³.
Step-by-step explanation:
Given : The open rectangular box of maximum volume that can be made from a sheet of cardboard 21 in. by 12 in. by cutting congruent squares from the corners and folding up the sides.
To find : The dimensions and the volume of the box?
Solution :
Let h be the height of the box which is the side length of a corner square.
According to question,
A sheet of cardboard 21 in. by 12 in. by cutting congruent squares from the corners and folding up the sides.
The length of the box is 
The width of the box is 
The volume of the box is 




To maximize the volume we find derivative of volume and put it to zero.


Solving by quadratic formula,




Now, substitute the value of h in the volume,

When, h=2.45


When, h=8.54


Rejecting the negative volume as it is not possible.
Therefore, The volume of the box is 280.05 in³.
The dimension of the box is
The height of the box is h=2.45
The length of the box is 
The width of the box is 
So, Dimension of the box is 