Explanation:

- Let's denote the third number as $x$.

- The second number is twice the third number, so it is $2x$.

- The first number is thrice the second number, so it is $3(2x)=6x$.

- The average of the three numbers is given as 45, which means:

$$

\frac{x + 2x + 6x}{3} = 45

$$

- Simplifying gives:

$$

\frac{9x}{3} = 45 \quad \Rightarrow \quad 3x = 45 \quad \Rightarrow \quad x = 15

$$

- Thus, the numbers are 15, 30, and 90.

- The difference between the first number (90) and the second (30) is 60.

Option 3: 60 is the correct choice.

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