This may be simple, but I don't know the answer.
I have the following data: (0,0) (1,12) (2,24) (3,30) (4,36) (5,42) (6,48) (7,54) and so on, the y coordinate increasing by 6 for values above 2 and by 12 for X values of 0, 1 and 2.
Is there a simple equation for that line? What should I be googling?
If you want to express it as a function, then you do so by defining the function piecewise:
$y = f(x) = \left \{ \begin{array}{ll} 12x & x \lt 12 \\ 6x + 12 & x \ge 12 \end{array} \right.$
Alternatively, you can write it using something like the Heaviside step function, but that's just doing exactly the same thing but hiding the piecewise nature of your function.