Using the scroll bar, scroll all the way to the right until you see Pluto. (It's the single pixel above the "u" in "Pluto.") Since that gives us the minimum size that can be seen, we can estimate that 1 pixel is the diameter of Pluto or 2,470 km.

If the resolution of a standard computer monitor is 72 dpi, how many km are in an inch? (72 dots/in) (2,470 km/dot)

Convert the answer into scientific notation: km/in

The distance to Pluto is 5.91 10⁹ km. The model must be at least that wide to fit the entire solar system. How many inches wide does the model have to be? (5.91 10⁹ km)/(____________________ km/in) = _____ in

Inches are an inconvenient unit for such a long distance, so lets convert it to feet: (____________________ in) (1 ft/12 in) = _____ft

That's still a very large number, so let's convert this to miles (there are 5,280 ft in a mi): (____________________ ft) (1 mi/52802 ft) =_____ mi