Volume of small box :
[tex]v=l\times b\times h\\\\v=2\times 3\times 4\\\\v=24\ units^3[/tex]
Volume of big box :
[tex]V=L\times B\times H\\\\V=12\times 21\times 40\\\\V=10080\ units^3[/tex]
Number of small boxes that can fit into bigger box :
[tex]n=\dfrac{V}{v}\\\\n=\dfrac{10080}{24}\\\\n=420[/tex]
Therefore , 420 such boxes can fit .
Hence , this is the required solution .
