Question 549028
Let's first solve for the time that is traveled before they meet.  
We will call this time t

We have the following formula 
{{{20*t+50*t=560}}}
{{{70*t=560}}}
{{{t=560/70}}}
{{{t=8}}}


So we need to find how far Mark traveled in 8 hours.  

If mark is traveling 20 miles per hour, and he traveled for 8 hours... I will let you do the rest (use these two pieces of information to find the distance-- it may help to look at how we added the distances earlier in the equation))

Let me know if you are still unsure:)