Help me please with this

Question

Pete discovered a new radioactive substance, and named it Vassilium. The half-life of Vassilium is 218 years. If he starts with 20 grams of the substance, write a function to represent the number of grams of Vassilium that will remain after x years. To the nearest tenth, how many grams of Vassilium will remain after 400 years?

find f(x)=

and # of grams

Answer 1

f(400) = 20(0.5)^400/218

f(400) ≈ 20(0.5)^1.83486)

f(400) ≈ 20(0.28)

f(400) ≈ 5.6