Correct Answer: Rs. 12,000

Solution : Time taken by the first person alone = 36 days
⇒ Part of work done by the first person in a day = $\frac{1}{36}$
Time taken by the second person alone = 48 days
⇒ Part of work done by the second person alone in a day = $\frac{1}{48}$
Let the time taken by the expert alone = $x$ days
⇒ Part of work done by the expert in a day = $\frac{1}{x}$
Time taken by all three working together = 12 days
⇒ Part of work done by all three in a day = $\frac{1}{12}$
According to the question,
$\frac{1}{36}$ + $\frac{1}{48}$ + $\frac{1}{x}=\frac{1}{12}$
⇒ $\frac{1}{x}=\frac{1}{12}-\frac{1}{36}-\frac{1}{48}=\frac{12-4-3}{144}=\frac{5}{144}$
⇒ Ratio of work done by Stanie, Paul, and the expert $=\frac{1}{36}:\frac{1}{48}:\frac{5}{144} = 4:3:5$
So, the amount received by the expert $=\frac{5}{4+3+5}×28800 = 5 × 2400 =$ Rs. $12000$
Hence, the correct answer is Rs. 12,000.