Ответ:

2345 = 2000 + 300 + 40 + 5 = MMCCCXLV.

1987 = 1000 + 900 + 80 + 7 = MCMLXXXVII.

MMCCXL = 1000 + 1000 + 100 + 100 + 40 = 2240.

DCLXX = 500 + 100 + 50 + 10 + 10 = 670.