Given data:
The given distance is d=120 mi.
The given speed of Mark is s=30 mph.
The given speed of Mark's friend is s'=50 mph.
The expression for the distance covered by Mark when he meet with his friend at any time t is,
[tex]x=30t[/tex]The expression for the distance covered by Mark's friend when he meet with Mark at any time t is,
[tex]120-x=50t[/tex]Substitute 30t for x in the above expression.
[tex]\begin{gathered} 120-30t=50t \\ 120=80t \\ t=1.5\text{ h} \end{gathered}[/tex]Thus, after 1.5 hours they meet.
