Help in Math - Graph

Radioactive substances decay over time. A certain radioactive substance has a half-life of 4 days, i.e. after 4 days only half of the original amount of substance is present.

Use the following formula;

f(t)=b*a^t,

1/2*b=b*a^t

I already have the following;

Growth factor, a=0.841

b = the initial factor

1/2*b = the half of the initial factor

Question;

c) What fraction of the initial amount of substance is still present after 2,3,4,6,8,10 days? (Prepare a table)

I don't know if the screenshot with the problem in German will help you.

As far as I am aware, I have to replace the t in the given formula with the number of days, however I am not sure. As I am not sure as to how to make the table.