Chromium-51 is a radioactive isotope used to label red blood cells to identify if they remain intact in the body. it has a half-life of 27.7 days. if 0.25 mg is an approximate dose amount, how much remains after 83.1 days?

Since the half life is the the time taken for half of the Chromium-51 to decay, for n half lives, the mass of Chromium-51 will fall to 1/(2^n) of its original value. 83.1/27.7 = 3 so the mass of Chromium-51 will fall by a factor of 1/(2^3) = 1/8.
0.25 mg / 8 = 0.031 mg (2 significant figures).

Iwould you figure it out but you don't have a picture or in your question as to what the physical property you're looking for is

Decomposition is the cycle at which bacteria breaks down any organic material into the soil