The question is ambiguous. Assuming "lived with his son around 50 years" means Sam was 50 when his son was born. Sam's Year of Death = 1955. Sam's Age at Death = ?. Son's Year of Birth = Sam's Birth Year + 50. Son's Year of Death = Son's Birth Year + 100. This cannot be solved. The keyed answer is 1875, which implies Sam lived to be 80.