Nowadays 789 expressed as a Roman numeral is DCCLXXXIX but the ancient Romans would have notated it quite differently.
DCCLXXXIX
((MCCXXXIV))(CDLVI)DCCLXXXIX
D
LV
MCXVII
16
V
That is 29.
3409 in Roman numerals is MMMCDIX
DCCCXXXII in roman numeral is 832.
10 = X in Roman numerals
LXX