ANSWER
About 51.8 ft
EXPLANATION
The trees and their shadows form similar triangles - since the shadow is made at the same time:
The ratio between the largest shadow and the smallest shadow is:
[tex]\frac{23}{8}[/tex]This ratio must be the same for the height if the trees, because the triangles are similar. Therefore, the height of the second tree is:
[tex]\begin{gathered} \frac{x}{18}=\frac{23}{8} \\ x=\frac{23}{8}\times18=51.75 \end{gathered}[/tex]
