That would actually depend on what you are measuring.

1200 months is equal to 100 years. 475 months is equal to 39 yrs, 7 months. 1200 months plus 475 months is equal to1675 months, which in terms of years would be 139 years, 7 months.

1200 centimetres (cms) is equal to 40 ft. 475 cms is equal to 15 ft, 25 cms. (almost 16 ft)

1200 cms (40 ft) + 475 cms ( 15 ft, 25 cms) is equal to 1675 cms which is equal to (40 ft + 15 ft, 25 cms) is equal to 55 ft, 25 cms.

Apply the above to inche's.

1200 inches is equal to 100 ft. 475 in is equal to 39 ft, 7in.

1200 in + 475 in is equal to 1675 in, which in turn, just as the months, is equal to 139 ft, 7 in.

1200 of anything + 475 of the same, is always equal to 1675 of whatever it is you are adding or solving.