Cars A and B are traveling toward each other at the same time from two places 272 kilometers apart. After 3 hours, the distance between the two cars is still 17 kilometers. Car A travels 45 kilometers per hour. How many kilometers per hour does Car B travel? What is the equivalence relationship between the quantities in the title.
甲、乙两车同时从相距272千米的两地相向而行，3小时后两车还相距17千米，甲车每小时行45千米，乙车每小时行多少千米？题目中数量间的相等关系是多少．
<result>3</result>