Read the excerpt from The Riddle of the Rosetta Stone by James Cross Giblin. He began with another cartouche from the same inscription and numbered each of the hieroglyphs in it.

Of the nine symbols, Champollion already knew numbers 1, 2, 4, 5, 7, and 8. When he lined up all the numbers and put the corresponding letters beneath them, he got the following arrangement:

1 2 3 4 5 6 7 8 9
A L S E T R

Immediately Champollion thought of the one Greek leader whose name might be identified with this particular combination of letters. It was Alexander the Great, spelled "Alexandros" in Greek, and apparently represented as "Alksentrs" in hieroglyphs.
Champollion filled in the gaps in the arrangement:

1 2 3 4 5 6 7 8 9
A L K S E N T R S

Based on the information in the excerpt, the reader can conclude that

Champollion knew that inscriptions on cartouches were often the names of famous leaders.
the ancient Egyptians spelled the names of leaders the same way that the Greeks did.
Champollion misspelled “Alexandros” because he incorrectly guessed some of the letters.
Alexander the Great knew how to write in both Greek and Egyptian hieroglyphics.