The decay constant of $$ ^{238}U$$ is $$4.9 \times 10^{-18} s^{-1} $$ (a) What is the average -life of $$ ^{238}U $$? (b) What is half-life of $$ ^{238}U $$? (c) By what factor does the activity of a $$ ^{238}U $$ sample decreases in $$ 9 \times 10^9 $$ years ?