Can you please solve the question as soon as possible.

Rate of a Reaction and Half-life 6. One of the hazards of nuclear explosions is the generation of 90Sr and its subsequent incorporation in place of calcium in bones. This isotope emits beta rays of energy 0.55MeV and has a half-life of 28.1 year. Suppose 1.4g was absorbed by a newly born child, how much will remain after (a) 18 years and (b) 70 years? (total 10 points) hint: radioactive disintegration is a first order process