Answer:
9, 30, and 15.
Step-by-step explanation:
Let the three numbers be a, b, and c.
The sum of them is 54. So:

The third number is 6 more than the first. In other words, c=a+6.
The second number is twice the third. In other words, b=2c.
Let’s write the second number in terms of a. Since b=2c, this means that b=2(a+6).
Let’s substitute them into our equation. So:

Solve for a. Distribute:

Combine like terms:

Subtract 18 from both sides:

Hence, the value of a is:

So, the first number is 9.
The third number is 6 more than the first, so the third number is 15.
The second number is twice the third. So, the second number is 30.
Therefore, our numbers are:
9, 30, and 15.