How do you figure the weight watchers formula out not using a calculator?

p=(c/50) + (f/12) - (min {r,4}/5)

p = points

c = calories

f = fat grams

r = dietary fiber

(Note: min{r, 4} equals the number of grams of dietary fiber or 4, whichever is smaller. In other Words, only the first 4 grams of fiber "count.")

ex. p = (100/50) + (8.75/12) - (2/5)

p = (2) + (.729) - (.4)

p = 2

c = 100

f = 8.75

r = 2