Explanation:

- Let the fourth number be \( x \).

- The third number is three times the fourth number: \( 3x \).

- The second number is 1.5 times the third number: \( 1.5 \times 3x = 4.5x \).

- The first number is one-third of the second number: \( \frac{1}{3} \times 4.5x = 1.5x \).

To compute the average:

- Add up all four numbers: \( x + 3x + 4.5x + 1.5x = 10x \).

- The average is given as 10: \( \frac{10x}{4} = 10 \).

- So, solving for \( x \): \( 10x = 40 \rightarrow x = 4 \).

Plugging back to find each number:

- Fourth number: \( x = 4 \).

- Third number: \( 3x = 12 \).

- Second number: \( 4.5x = 18 \).

- First number: \( 1.5x = 6 \).

Answer: Option: 2 - 18