We have the following equation:
Q = Qo * exp (-k * t)
Substituting values we have:
20 = 24 * exp (-0.00011 * t)
We clear the value of t:
exp (-0.00011 * t) = 20/24
We apply Neperian logarithm to both sides:
ln (exp (-0.00011 * t)) = ln (20/24)
-0.00011 * t = ln (20/24)
t = ln (20/24) / (- 0.00011)
t = 1660 years
Answer:
t = 1660 years