Answer :
Applying Pythagoras theorum to the situation ;
[tex] \alpha ^2 + \beta ^2 = C^2 \\ \\ 9^2 + \beta ^2 = 15^2 \\ \\ 81 + \beta ^2 = 225 \\ \\ => \beta ^2 = 144 \\ \\ => \beta = 12 cm[/tex]
Thus, the answer is 12 ft.
[tex] \alpha ^2 + \beta ^2 = C^2 \\ \\ 9^2 + \beta ^2 = 15^2 \\ \\ 81 + \beta ^2 = 225 \\ \\ => \beta ^2 = 144 \\ \\ => \beta = 12 cm[/tex]
Thus, the answer is 12 ft.