How do you find the percent of increase from 12 to 18?

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.