Question 648179
Let t = the amount of time the planes travel
Let d1 = distance travelled by east bound plane
Let d2 = distance travelled by the west bound plane
Formula to use
(1) d = r*t, where d is the distance travelled, km, in time t, hr, when travelling at a rate of r km/hr
For the first plane
(2) d1 = 560*t
For the second plane 
(3) d2 = 640*t
The total distance travelled or distance apart after t hr is
(4) d1 + d2 = 2100
Substituting (2) and (3) into (4) yields
(5) 560*t + 640*t = 2100 or
(6) 1200*t = 2100 or
(7) t = 7/4
Answer: The planes will be 2100km apart at 12:15pm.