The exact form is x= -3/14
Okay here:
Let L be the length and W the width of the rectangle.
1. w=2•L
2. 2L+2W=36
Substitute eq. 1 into eq. 2,
2L+2•(2•L)=36
2L+4L=36
6L=36
L=9
Not done yet, then from eq. 1,
W=2•L
W=2•9
W=18 <------- Your answer. :)
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.
Starting off, we can multiply the third equation by 2 and add it to the third to get rid of both the x and y variables. Next, we get z=1. Plugging that into 3y-5z=-23, we get 3y-5=-23. Adding 5 to both sides, we get 3y=-18. After that, we can divide both sides by 3 to get y=-6. Plugging that into -2x-y-z=-3, we get -2x+6-1=-3=-2x+5. Subtracting 5x from both sides, we get -2x=-8. After that, we can divide both sides by -2 to get x=4.
I’m not positive but i think it’s 36x^2 -1