Let's get the data out of the problem:
Nv = 18
Ov = 12
Now, we can apply in this equation that relates the new and the old values:
i = Nv / Ov
i = 18 / 12
i = 1.5
Now, we just consider what has passed from 1, and this is 0.5, converting to percentage it is:
p = 0.5 . 100
p = 50%
The increase was 50%.
Hope it helps.
