Answer:
-62.45m/s and +62.45m/s
Explanation:
The formula for relativistic speed
This is the speed of A with respect to B
[tex]V_{AB}=\frac{V_{A}-V_{B}}{1-\frac{V_{A}V_{B}}{C^2} }[/tex]
where
[tex]V_{A}[/tex] will be the velocity of person 1: 39m/s
[tex]V_{B}[/tex] will be the velocity of person 2: -31m/s (negative because is travelling in opposite direction)
and [tex]C[/tex] the velocity of light: 100m/s
The velocity of person 1 measured by person 2 is:
[tex]V_{AB}=\frac{39m/s-(-31m/s)}{1-\frac{(39m/s)(-31m/s)}{(100m/s)^2}}=62.45m/s[/tex]
The velocity of person 2 measured by person 1 is:
[tex]V_{BA}=\frac{V_{B}-V_{A}}{1-\frac{V_{B}V_{A}}{C^2} }[/tex]
[tex]V_{BA}=\frac{-31m/s-39m/s}{1-\frac{(-31m/s)(39m/s)}{(100)^2} }=-62.45m/s[/tex]
