Please read the following table in Markdown format and then answer the question according to the table. Table cells in one row are seperated by '|', and different rows are seperated by '
'.

Table:
| Number | Builder | Type | Date | Works number | Notes |
| --- | --- | --- | --- | --- | --- |
| 51 | Baldwin Locomotive Works | DS4-4-750 | 1949 | 74408 | Acquired new 1949, Retired 1970/Wrecked-Scrapped. |
| 52 | Baldwin Locomotive Works | DS4-4-750 | 1949 | 74409 | Acquired new 1949, retired in 1970 and scrapped in 1990 |
| 53 | Baldwin Locomotive Works | DS4-4-1000 | 1949 | 74193 | ex-Pan American Engineering W8380; née Army Corps of Engineers W8380, acquired 1956, retired in 1985, to John Bradley, 1985; to Roots of Motive Power Collection |
| 54 | Baldwin Locomotive Works | S-12 | 1952/1953 | 75823 | ex-NW (3307); née WAB 307, wrecked 1968, retired 1970, scrapped |
| 55 | Baldwin Locomotive Works | RS-12 | 1955 | 76024 | decorated for the United States Bicentennial\n\n\nnee MR 32, acquired 1968, scrapped 1995 |
| 56 | Baldwin Locomotive Works | RS-12 | 1955 | 76105 | nee MR 33, acquired 1970, retired 1985 to John Bradley, 1985; to Travel Town Museum (Los Angeles, CA)56 |
| 57 | Baldwin Locomotive Works | S-12 | 1953 | 75914 | nee SP 1539, acquired 1970, retired unknown, stored at Willits, California |
| 61 | American Locomotive Works | RS-11 | 1979 | Unknown | Former SP. Status Unknown |
| 62 | American Locomotive Works | RS-11 | 1979 | Unknown | Former SP. Status Unknown |
| 63 | American Locomotive Works | RS-11 | 1979 | Unknown | Former SP. Sold to NVRR 1987 |
| 64 | Electro-Motive Diesel | GP9m | 1987 | Unknown | Former SP # 3411. Operational and in regular service |
| 65 | Electro-Motive Diesel | GP9m | 1987 | Unknown | Former SP # 3412. Operational |
| 66 | Electro-Motive Diesel | GP9m | 1956 | Unknown | Former C&O # 6145. Acquired 1998. Operational and in regular service. |
| 67 | Electro-Motive Diesel | GP9m | 6/1954 | 19554 | built as Bangor and Aroostook Railroad # 77; acquired 1998; never delivered |
| M-80 | Mack | Railbus | 1923 | Unknown | Purchased 1925. Wrecked twice: in 1957 with a delivery truck, and in 1964 with M-100. Scrapped 1964 |
| M-100 | Edwards Rail Car Company | Motor Car | 1925 | Unknown | Acquired from Moorhead & North Forks Railroad; Operable. Recently repainted back to historic yellow scheme |
| M-200 | SS&IW | Motor Car | 1927 | Unknown | Ex-TRC #22; née-LPN 20; to Niles Canyon Railway, 1975; Operable on Niles Canyon Railway |
| M-300 | American Car and Foundry Company | Motor Car | 1935 | Unknown | M-300 at Fort Bragg\n\n\nEx-SLGW; née AR; Operable |
Question:
how long was the locomotive type ds4-4-750 in service with the railroad?
Answer:
21 years