chemistry
posted by Peter .
The halflife of stronitum90 is 28 years. How many grams of this nuclide in a 4.00g sample will remain after 112 years?

k = 0.693/t_{1/2} = 0.693/28 = ??
Substitute for k in the equation below.
ln(No/N) = kt
ln(4.00/N) = k(112)
Solve for N.