Answer :
Assume that the height of the tower is x
Since the shadow of x is 21 feet
Since the shadow of 10 feet is 8 feet
By using the equal ratio between the actual heights and their shadow
[tex]\frac{x}{21}=\frac{10}{8}[/tex]By using the cross multiplication
[tex]\begin{gathered} x\times8=10\times21 \\ 8x=210 \end{gathered}[/tex]Divide both sides by 8 to find x
[tex]\begin{gathered} \frac{8x}{8}=\frac{210}{8} \\ x=26.25\text{ f}eet \end{gathered}[/tex]The height of the tower is 26.25 feet