Question 1046165
UNKNOWN:  
t, time for Chelsea's travel to catchup
d, catch-up distance
KNOWN:
R=12 mph
r=6 mph
h=3, for "three hours later"


<pre>
              speed      time        distance
Dianna         r          t+h           d
Chelsea        R           t            d
</pre>

The question basically asks for t.
Travel Rate rule is RT=D to relate RATE, TIME, DISTANCE;
You will only need to form one equation because d is the same value for Dianna and for Chelsea - the catchup distance.