Which object best represents a true scale model of the shape of the earth?

Any object that is spherical in shape would best represent a true scale model of the shape of the Earth.

for example: ping pong balls, billiard balls, marble and other smooth spherical objects. The shape of the Earth is called the oblate spheroid.

try using substitution:

x + y - 6 = x - y. (i'm not giving you the exact answer). since 0 = x - y, then sub 0 in the equation with x - y. combine your like terms, and then use inverse operations, and you'll have your answer.

: -)

what bodys are there orbiting?