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