Examine why they work ?
Choose a number. Double it. Add nine. Add your original number. Divide by three. Add four. Subtract your original number. Your result is seven.

Answer

Let your original number be n. Then we are doing the following operations: `n to 2n to 2 +9 to + n = 3n + 9 to (3n+9)/3 = n + 3 to n + 3 + 4 = n+ 7 to n + 7 - n=7`