Question 418530
average speed =x
time = y

..
xy=2400
x=2400/y
(x+6)(y-14/60)= 2400
(x+6)(60y-14)/60=2400
(x+6)(60y-14)=60*2400
plug x
(2400/y +6)(60y-14)=60*2400
(2400+6y)(60y-14)/y=144000
(2400+6y)(60y-14)=144000y
6(400+y)*2(30y-7)=144000y
(400+y)(30y-7)=144000y/12
12000y-2800+30y^2-7y=12000y
30y^2-7y-2800=0

solve using quadratic formula
b^2-4ac=336049
...
y=9.78 hours
x=2400/9.78 = 245.4 mph