When will these two trains meet each other I cant seem to solve this problem. 


A train leaves point A at 5 am and reaches point B at 9 am. Another train leaves point B at 7 am and reaches point A at 10:30 am.When will the two trains meet ? Ans 56 min 


Here is where i get stuck.
I know that when the two trains meets the sum of their distances travelled will be equal to the total sum , here is what I know so far
Time traveled from A to B by Train 1 = 4 hours
Time traveled from B to A by Train 2 = 7/2 hours
Now if S=Total distance from A To B and t is the time they meet each other then
$$\text{Distance}_{\text{Total}}= S =\frac{St}{4} + \frac{2St}{7} $$ 
Now is there any way i could get the value of S so that i could use it here. ??

Since both trains move toward each other when remaining half of a space,
then the general meeting equation in t is:
$$v_{1}*t + v_{2}*t = S$$
Then we get that:
$$ \frac{S t}{4}+\frac{2S t}{7}=\frac{S}{2} \longrightarrow  \frac{ t}{4}+\frac{2t}{7}=\frac{1}{2} \longrightarrow t=\frac{14}{15} (\text{56 minutes})$$
Q.E.D.
