Question

Two planes start from los angeles international airport and fly in opposite directions. the second plane starts 1/2 hour after the first plane, but its speed is 60 kilometers per hour faster. find the airspeed of each plane if 2 hours after the first plane departs, the planes are 3135 kilometers apart.

Answer 1

Let x = first plane's speed.  
We have the equation:
 2 hours * x km/h + 1.5 hours * (x+60) km/h = 3135 km. 
 3.5 hours*x km/h + 90 km = 3135km
 3.5hours*x km/h = 3045km 
 x = 870 km/h. 
 The first plane is traveling at 870 km/h, therefore since it is 60 km/h faster, the second plane is traveling at 930 km/h.