Correct Answer: 0.288

Solution : Given: The numbers = 0.3, 0.8 and 0.108
Let the fourth proportion be $x$.
We know that,
If $a ∶ b = c ∶ d$; then $d$ is called the fourth proportional to $a, b,$ and $c$
⇒ $\frac{a}{b}=\frac{c}{d}$
⇒ $\frac{0.3}{0.8}=\frac{0.108}{x}$
⇒ $x=\frac{0.108\times0.8}{0.3}$
⇒ $x=\frac{0.108\times0.8}{0.3}$
= 0.288
Hence, the correct answer is 0.288.