If s = 2x + t/r what is x in terms of r, s, and t? A) x= rs/ 2-t
B) x= rs-t/ 2
C) x= 2rs-t
D) x= rs-2t

An equation for the ellipse ( standard form ):
x²/a²  +  y²/b² = 1
Here is:  a - semi-major axis and b - semi-minor axis.
Radius of the moon is 1,000 km and the distance from the surface of the moon to the satellite varies from 953 km to 466 km.
a = 1,000 + 953 = 1,953 km
b = 1,000 + 466 = 1,466 km

The equation is  x² / 1,953²  + y² / 1,466² = 1
or: x²/3,814,209  +   y²/2,149,156  = 1