The correct answer is (D) 36 m.
Using similarity of triangles (AA criterion), the ratio of height to shadow length is constant:
$$\frac{7.5}{5} = \frac{h}{24} \Rightarrow h = \frac{7.5 \times 24}{5} = 36 \text{ m}$$
At the same time of day, the sun's rays are parallel, so a vertical pole and a tower cast shadows that form equiangular (similar) triangles with the ground. This means height/shadow ratios are equal. Set up the proportion and solve for the unknown height. This is a direct application of the AA similarity criterion from Chapter 6.