What is the equation that models the sequence 6,12,24,48

The equation that models the sequence is: 6+6 each time.

To see what equation gives us the sequence, let's first try to find a pattern.
6 to 12 can be: x + 6, 2x, 3x -6.
12 to 24 can be: x + 12, 2x, 3x -12.
24 to 48 can be: x + 24, 2x, 3x - 24.
Let's see if we can find a common pattern.
2x is a common pattern.
Your equation is : 
n = 2x.
I hope this helps!