The equation of a circle:

(h, k) - center
r - radius
Look at the picture:
center: (4, -2) → h = 4, k = -2
radius: r= 5
Substitute:

Answer:
x=10/27
Step-by-step explanation:
just add the E's on one side than move over the other E than move 14 to the 4 by minusing it
"He starts both trains at the same time. Train A returns to its starting point every 12 seconds and Train B returns to its starting point every 9 seconds". Basically, what you need to do is find the least common multiple. The least common multiple of 12 and 9 is 36, so the least amount of time, in seconds, that both trains will arrive at the starting points at the same time is 36 seconds.