I've just been really thrown off by what this problem is asking me.

Given:

The decay of a radioactive material may be modeled by assuming that the amount A(t) of material present (in grams) at time t (minutes) decays at a rate proportional to the amount present, that is dA/dt= -kA for some positive constant k. Every subpart of this question refers to exactly the same radioactive material.

Question:

a. derive an equation for the amount A(t) present at time t in terms of the constant k and the amount A(o) present at time t=0

b. if A(5) = 1/3A(3), find K

c. at what time t will the amount A(t) be 1/4A(0)

My attempt (?):

for part a I wasnt sure if it was referring to just giving the equation A(t)=A(0)e^-(kt)

and I have no idea how to go about b or c. please help me if possible ! I think i'm over thinking the problem. I'm just really thrown off by the lack of numbers. Thank you!