Question

In a model the distance from the sun to earth is 7 inches and the distance from the sun to Neptune is 19 inches.

Answer 1

If in the model the distance from the Sun to Earth is scaled down to 7 inches, and the distance from the Sun to Neptune is scaled down to 19 inches, then the scale is approximately 7/19 = 0.368.

This means that each inch in the model represents roughly 0.368 astronomical units (AU) in reality.