Question 47556
This is a problem of related rates.
The most important information, and the easiest to miss,
is at the very end. 
They meet.
Each has traveled the same distance, since they started
at the same place.
Let {{{d(m)}}} = Martina's distance
Let {{{d(j)}}} = John's distance
{{{d(m) = d(j)}}}
so, just call the distance {{{d}}}
{{{t}}} = Martina's time
When they meet, John's time will be 2 hours less
{{{t - 2}}} = John's time
24 = Martina's rate
48 = John's rate
{{{d = 24t}}}
{{{d = 48*(t - 2)}}}
{{{24t = 48*(t - 2)}}}
{{{24t = 48t - 96}}}
{{{24t = 96}}}
{{{t = 4}}}
So, Martina's time is 4 hours and JOhn's time is {{{4 - 2}}} hours
or 2 hours. If Martina left at 9 AM, then 4 hours later, it will
be 1 PM (answer)