Researchers are monitoring two different radioactive substances. they have 300 grams of substance a which decays at a rate of 0.15%. they have 500 grams of substance b which decays at a rate of 0.37%. they are trying to determine how many years it will be before the substances have an equal mass.

if m represents the mass of the substance and t represents the elapsed time in years, then which of the following systems of equations can be used to determine how long it will be before the substances have an equal mass?
a.

b.

c.

d.