Answer:
Incomplete question, but you can use the formulas given to solve it.
Explanation:
Uniform probability distribution:
An uniform distribution has two bounds, a and b.
The probability of finding a value of at lower than x is:

The probability of finding a value between c and d is:

The probability of finding a value above x is:

Uniform distribution over an interval from 0 to 0.5 milliseconds
This means that

Determine the probability that the interarrival time between two particles will be:
Considering
, and the question asked, you choose one of the three formulas above.