|Number|Builder|Type|Date|Length|Notes|
|---|---|---|---|---|---|
|51|American Car Company|Motor|1904|47'9"|retired 1933|
|53|American Car Company|Motor|1904|47'9"|retired 1933|
|55|American Car Company|Motor|1904|47'9"|became inspection car in 1932 retired 1941|
|57|American Car Company|Motor|1904|47'9"|became inspection car in 1932 retired 1941|
|59|W. L. Holman Car Company|Motor|1904|44'|retired 1932|
|61|W. L. Holman Car Company|Motor|1904|44'|retired 1932|
|63|W. L. Holman Car Company|Motor|1904|44'|retired 1932 preserved Western Railway Museum|
|65|W. L. Holman Car Company|Motor|1904|44'|retired 1932|
|67|W. L. Holman Car Company|Motor|1904|44'|retired 1932|
|69|W. L. Holman Car Company|Motor|1904|44'|converted to express trailer in 1919 retired 1932|
|71|W. L. Holman Car Company|Trailer|1905|44'|retired 1929|
|73|W. L. Holman Car Company|Trailer|1905|44'|retired 1929|
|01|W. L. Holman Car Company|Express Trailer|1916||built as #8 express motor demotorized 1917 designated express trailer 1920 retired 1933|

Question: what was the number of cars built by american car company?
Answer: 4