Answer
We can rank the samples according to their half-life:
$A = C \gt B$
Work Step by Step
On the graph we can see that the time it takes sample B to decrease to half its original value is less than the time it takes the other two samples. Thus sample B has the shortest half-life.
On the graph we can see that the time it takes sample A and sample C to decrease to half the original value is equal. Thus sample A and sample C have the same half-life.
We can rank the samples according to their half-life:
$A = C \gt B$
