Since the problem states "a number" and again "a number", I assume it;'s the same number. Let the number be x.
12x - 9x = 3x
The difference of twelve times a number and nine times a number is three times the number.
When the rocket accelerates up, the thrust is greater than the combined lift and drag, therefore making it go upward. Thrust from the engine / or whatever the power source is makes it lift.
Hope that helps!
This is what I got use photo math
