The half life of Polonium-210 is 140 day and a sample of this element has a mass of 300 mg

Find the mass that remains after t days

y= f(t)

initial amount is 300 mg

f(t)= 300e^kt

To determine the value of k we use the fact that half life is 140d and so

f(140)= 150 thus

300e^140k=150

I am confused on how they get f(140) = 150?

since f(140)=300e^140k=/= 150??