For once something easy to answer
I did this stuff last week in school
It is basically percent of change
The formula is %=c/o in other words it is percent equals change over original
12 is the original and 50 is the new price or whatever
Now do 50-12=38 then do 38/12 in other words thirty-eight over twelve
Then 38 divided by 12 which equals 3.16666666... the six will keep repeating so we round to the nearest percent
316 with the six repeating %
There you go, that is how I was taught
