Radioactive Decay: Calculating Plutonium Amount & Age of Meteor

[CharlieW95]

Homework Statement

A meteor contains 2.45kg of plutonium-239. It has a half-life of 24065 years. Calculate:
a) The number of plutonium molecules currently present in the meteor (at. mass = 239.052)
b) How long ago the meteor struck the Earth if originally it contained 10kg of plutonium.

Homework Equations

no.atoms= mass/(atomic mass) x avagadro^' s no.(6.02x〖10〗^23)

N = No e-γt
where the decay constant, γ(gamma), and T1/2 are related by
γT1/2 = ln(2)

The Attempt at a Solution

I solved A, and achieved an answer of 6.16979x1024 particles.
I'm confused as to where to go from here.

 

[SHISHKABOB]

just obtain a value for γ, substitute it into N = No e^(-γt) and solve for t