can someone please help me with this physics problem?

Question

a radioactive substance decays in such a way that the amount of mass remaining after (t) days is modeled by the function m(t)=5e^-.015t. where m(t) is measured in kg's, find the mass at t=0 and the amount of mass remaining after 40 days in kgs.?

Answer 1

m(t) = 5 e ^(- 0.015 t)

m(0) = 5 kg

m(40) = 5 e ^(- 0.015 x 40)
m(40) = 5 e ^(- 0.6 )
m(40) = 2.74 kg

Answer 2

First, substitute t=0 into the equation.

You get m(t) = 5 e^0 = 5*1 = 5 kg.

Then, substitute t=40 into the equation.
You get m(t) = 5 e^(-0.15*40) = 5 e^-6 which surely you can calculate.