Cheat Engine

[Trucido]

Or are the answers incorrect?

Heres the question:
The time for a beam of light from an observer to a mirror and back was measured to be 5.511×10^-5 seconds using Fizeau's original apparatus. If the mirror and the observer were 8663 m apart, calculate the speed of light according to these measurements.

Ok so,
Time = 5.511x10^-5 (Or 5.511E^-5 Depending on how you like to write it)
Distance = 8663m

And Speed = Distance/Time

So it should be 8663/5.511x10^-5
Which gives 157194701.5 (1.57195×10^8 )

But occording to the answers, the correct answer is 3.144x10^8 m/s

Am I right and the book wrong? Or is the book right, and me wrong?

[Tofu]

You calculated the speed from the observer to the mirror.
You were supposed to calculate it to the mirror and back.

So the distance is doubled; 8663*2 = 17326

[Trucido]

You were on the right track, I worked it out.
I the time was to the mirror and back so all I had to do was halve the time then divide by the distance.