The formula for K-Argon dating is:
 

t - T (super 1.505)*log(No/N)/0.301 = years left

Potassium (super 40a)

1.3 x 10 (super 9) Argon 40 (12%)
 

while Carbon 14's formula is:

Carbon 14 5.72 x 10 (super 3) Nitrogen (super 14)