Question 834486
Two Unknowns:
r = speed of propeller plane
t = time for propeller plane
constants:
k = 90 mph, a speed difference
h = 4 hour, how much less time needed of the jet
d = 5670 mile trip



PLANE___________speed_________time______________distance
JET_____________r+k___________t-h_______________d
PROPELLER_______r_____________t_________________d


I have already solved a few of this general form travel problem recently, so this will be a very abbreviated solution.


EQUATIONS:
{{{highlight_green((r+k)(t-h)=d)}}} and {{{highlight_green(rt=d)}}}
Solve this system for r and t.  You will get a quadratic equation in either t or r.  The way I have solved these, I substituted for t from the simpler equation and first solved for a formula for r.  The quadratic equation I had used was in r.