320, half life = 160 units after 4 years and the equation is
(new)=(original)ek(time) so it becomes 160=320ek(4),
then 1/2=ek4, and to find the value after 12 years u use this:
y = 320ek(4)3 [since 4×3=12], then since we already know
1/2=e^k(4), then we substitute into the general equation and it
becomes Y = [320(1/2) ^ 3] and use the calculator to find the
answer. solved =)
