The speed is the ratio between the distance and the time:

Data:
d=6343miles
t=9h

Then, the plane traveled at a speed of 704.77 miles per hour.
Answer:
if you're trying to solve -35x= 18 .. then do the following
Step-by-step explanation:
x = -18 / 35
x= -0.5142857143
I'm guessing that b/c the answer is not an easy number that you probably are trying to do something else. .. ask again :)