Answer
0.57 g
Work Step by Step
Initial mass $N_{0}=1.55\,g$
$k=\frac{0.693}{t_{1/2}}=\frac{0.693}{3.8\,days}=0.18237/day$
$t= 5.5\,days$
$N=N_{0}e^{-kt}=1.55\,g[e^{-(0.18237/day)(5.5\,day)}]=0.57\,g$
($\frac{N}{N_{0}}$ is the ratio of the final to the initial number of atoms, but as mass is proportional to the number of atoms, $\frac{N}{N_{0}}$ can also be the ratio of final to the initial mass.)
