The ln 2 stands for the natural logarithm of two and can be estimated as 0693 and the l is the decay constant. For example if 100mg of a drug with a half-life of 60 minutes is taken the following is estimated. At first glance it may seem that not enough information was provided to solve this problem.
On the other hand if the half life is 4 minutes then each tick mark on the graph represents 4 minutes.
Plutonium 239 has a half-life of 24100 years. And in 9 hours. A P12 td. The half-life of a drug is an estimate of the period of time that it takes for the concentration or amount in the body of that drug to be reduced by exactly one half 50.