Answer: 36
Explanation:
As this is a two-digit number, it will have a digit in its 10's place and a digit in its 1's place. We can represent the 10's digit using x and the 1's digit using y.
Since the ones is twice the number of tens, this means that y is equal to 2*x. Let's put this into an equation.

If the 10's digit is x and the 1's digit is y, the original number would be
, as x must be multiplied by 10 to get it to the 10's place. Similarly, the reversed number would be
, as y must be multiplied by 10 to get it to the 10's place.
Twice the original number (10x+y) is equal to 9 more than (i.e. 9 plus) the reversed number. We can put this into an equation to help us answer the question.

Now we have a system of two equations.

We can solve this system by substituting y for 2x in the second equation. Then, we can isolate and get the value of x.

Now that we have the value of x, let's put it back into the first equation and solve for y.

Remember that x is the 10's digit and y is the one's digit of our answer. Since x is 3 and y is 6, our answer is 36.
Checking
We can quickly check if our answer is right by making sure both conditions in the question are met.
6 (the one's digit) is twice the value of 3 (the ten's digit), making the first condition true. Twice of 36 is 72, which is 9 more than the reversed number, which is 63.