Let the SECOND quantity mentioned (i.e., the "other group"'s rate, i.e., the
slower group's rate, be the one to represent by the letter for its unknown
quantity.  

So let r = the slower group's rate

Then use the sentence again to define the FIRST mentioned group's rate in
terms of the second one mentioned in the sentence.

So the first (faster) group's rate is r + 1.5

Their approach rate is the sum of their rates, which is r + r + 1.5 or
2r + 1.5

Then it's just 

DISTANCE =    RATE   x TIME
    |          |     |  | 
  1050   = (2r + 1.5)∙(200)


Solve that for the rate of the slower group, then add 1.5 mi/h to get the
rate of the faster group.

Edwin