A threshing floor is 50 meters long and 40 meters wide. After expansion, the length increases by 15 meters and the width increases by 13 meters. Calculate how much the area of the threshing floor has increased?
一个打谷场，长50米，宽40米，扩建后长增加15米，宽增加13米．算一算打谷场的面积增加了多少？
<result>17_000</result>