How do I solve this problem?

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 it's speed is 40 kilometers per hour faster. Find the speed of each plane when 2 hours after the first plane departs the planes are 2869 kilometers apart.

Answer 1

1st plane: (x+40)*2

2nd plane: x*3/2

2(x+40) + (3/2)x = 2869

2x + 80 + (3/2)x = 2869

(7/2)x = 2789

x =796 and 6/7

and

836 and 6/7

(745 and 3/7)* 3/2 + (785 and 3/7)*2 =