Question 1052086
rt = d (rate*time = distance)
r = d/t
8x(1.5) = 8x+420
12x = 8x+420
4x = 420
x = 105 was the speed of the slow plane, and
105*1.5 = 157.5 was the speed of the fast plane
------------------------------
Check - In 8 hours:
157.5*8 = 1260  
105*8 .  = 840
Difference:420 Correct
:
John