First the easy way.  You can do it in your head. 
They are separating at the rate of 60+50 or 110 mi/h.  
So at that rate it would take them 3 hours to be 
separated by 330 miles. That would be at 1PM.

But your teacher doesn't want you to do it this easy way.
So here is the way your teacher wants you to do it:

Let t = the number of hours after 10 AM when 
they will be 330 miles apart

Make this DRT-chart:

         Distance  Rate  Time
1st car                      
2nd car                       

They both travel the same length of time. So fill in
t for both times.

         Distance  Rate  Time
1st car                    t
2nd car                    t

Their rates are 60 and 50, so fill those in for the
rates.

         Distance  Rate  Time
1st car             60     t
2nd car             50     t

Now use D=RT to fill in the distances:

         Distance  Rate  Time
1st car     60t     60     t
2nd car     50t     50     t

Now the sum of the two distances must equal 330 miles.

So we have the equation:

60t + 50t = 330
     110t = 330
        t = 3

So it will take 3 hours after 10AM, or 1PM.

Edwin