The fourth proportional to 5, 8, 15 is:

Answer: Option B

$$\begin{array}{rl}& \text{Let}\text{the}\text{fourth}\text{proportional}\text{to}5,8,15\text{be}x\\ & \text{Then},5:8:15:x\\ & \Rightarrow 5x=8\times 15\\ & x=\frac{8\times 15}{5}=24\end{array}$$