YOU SAID:

if a train is moving at 50 miles an hour and you throw a baseball at 7 miles an hour how fast is the baseball

INTO JAPANESE

電車が時速50マイルで移動していて、野球を時速7マイルで投げる場合

BACK INTO ENGLISH

When the train is moving at 50 mph and throwing baseball at 7 mph

INTO JAPANESE

電車が時速50マイルで移動し、時速7マイルで野球をしているとき

BACK INTO ENGLISH

When the train is moving at 50 mph and playing baseball at 7 mph

INTO JAPANESE

電車が時速50マイルで動いていて、時速7マイルで野球をしているとき

BACK INTO ENGLISH

When the train is moving at 50 mph and playing baseball at 7 mph