Strontium-90 is one of the products of the fission of uranium-235. This strontium isotope is radioactive, with a half-life of 28. how many years will...

Strontium-90 is one of the products of the fission of uranium-235. This strontium isotope is radioactive, with a half-life of 28.1 yr. how many years will it take for 1.00 g of the isotope to be reduced to 0.200 g by decay. please include formula and please explain solution. thanks