The number is 10.5
Here's an explanation:
Let x represent the number. Twice x is equal to 2x. The problem says that 2x/7 = 3. So you multiply both sides by 7 so that you get rid of the constant, and you get 2x=21. Now to isolate the variable so you can get the answer, you divide each side by 2, so you get x=10.5. Since x represents the unknown number, the number is 10.5
