The living room of Wang Yuan's house is 6 meters long and 4 meters wide. Now there are two kinds of floor tiles, one with a side length of 20 cm and a unit price of 4 yuan; the other with a side length of 50 cm and a unit price of 7 yuan. Which floor tile is cheaper to choose for actually laying floor tiles?
王源家的客厅长6米，宽4米．现在有两种地砖，一种边长20厘米，单价4元：另一种边长50厘米，单价7元．实际铺地砖要选哪一种地砖比较便宜？
<result>50</result>