A substance with a half life is decaying exponentially. If there are initially 12 grams of the substance and after 2 hours there are 7 grams, how many grams will remain after 3 hours? Round your answer to the nearest hundredth, and do not include units.

Rick is driving to his uncles house in greenville,which is 120 miles from ricks town .after covering x miles rick she's a sign stating that greensville is 20 miles away. which equation when solved will give the value of x. a: x+120 = 20 b: x x120 =20 c: x +20 equals 120 d: x x20= 120