一辆卡车可以装21吨货物。要运840吨货物，需要几辆这样的卡车？-f*U/r:f'd't-v8Y;i1F+i5R:W4C
算式：提示9z7A2}:Y4W4X*\8]-f*U/r:f'd't-v8Y;i1F+i5R:W4C
答：需要.[,[2B:Q;Q8L)M)o辆这样的卡车.-f*U/r:f'd't-v8Y;i1F+i5R:W4C