Step-by-step explanation:
Initial dimensions of the storeroom were [tex]21\text{ }ft[/tex] length, [tex]15\text{ }ft[/tex] width and [tex]11\text{ }ft[/tex] height.
The room is in the shape of a cuboid. Volume of a cuboid = [tex]V=l\times b\times h[/tex], where [tex]l,b,h[/tex] are the length, width and height of the cuboid.
So, Volume of storeroom initially = [tex]21\text{ }ft\text{ }\times15\text{ }ft\text{ }\times11\text{ }ft\text{ }=3465\text{ }ft^{3}\text{ }[/tex]
Finally, the length was increased to [tex]25\text{ }ft[/tex] and width to [tex]17\text{ }ft[/tex].
Final volume of storeroom = [tex]25\text{ }ft\text{ }\times 17\text{ }ft\text{ }\times 11\text{ }ft\text{ }=4675\text{ }ft^{3}\text{ }[/tex]
Increase in volume = [tex]4675\text{ ft}^{3}-3465\text{ ft}^{3}=1210\text{ ft}^{3}[/tex]
∴ 1210 cubic feet of storage was added.