Radioactive isotope #1 has been kept for 1.5 years. originally, there were 100 grams and now there are 99.39 grams. when will there be 1 gram left?

This is an example of radio active decay
A(t) = A0e^(kt)
where A(t) is the amount of substance in time
A0 is the initial amount
k is the constant
t is the time
fist solve the value of k

99.39 = 100e^(1.5k)
k = -4.08 x 10^-3

t required to have 1 g is
1 = 100e^(-4.08 x 10^-3t)
solve for t
t = 1129 years