Special Theory Of Relativity

Two observers and observe two events and . The observers have a constant relative speed of 0.5c. In the units, where the speed of light, , is taken as unity, the observer obtained the following coordinates:
\text{Event P: } x = 5, y = 3, z = 5, t = 3
\text{Event Q: } x = 5, y = 1, z = 3, t = 5
\text{The length of the space-time interval between these two events, as measured by , is . The value of (in integer) is .}