The lamppost and Tad create similar right triangles. Set up a proportion comparing their equivalent sides.
[tex] \frac{lamppost height}{lamppost shadow} [/tex]= [tex] \frac{tad height}{tad shadow} [/tex]
[tex] \frac{x}{24} [/tex] = [tex] \frac{6}{15} [/tex]
Crossmultiply to solve.
24*6 = 15*x
144 = 15x
x = 9.6 feet