Master Zhang drove to deliver the goods. At the starting point, he saw the two-digit number on the milestone on the roadside as AB kilometers. One hour later, he saw the two-digit number on the milestone: BA kilometers. After another hour, he saw the milestone. The number on is a three-digit number, and it happens to be the middle of the two-digit number on the first milestone plus a 0: AOB km. What is the speed of Master Zhang in kilometers per hour?
张师傅开车去送货，在起点处他看见路边的里程碑上的两位数为AB千米，1小时后他看见里程碑上的两位数为：BA千米，又过1小时，看见里程碑上的数为三位数，且恰好是第一个里程碑上的两位数中间加上一个0：AOB千米．张师傅的车速为每小时多少千米．
<gadget id="calculator">61 - 16</gadget>
<output>45</output>

<result>45</result>