A bicycle shop owner adds 3 bikes to her stock every week. After 1 month, she had sold 18 bikes but still had 45 bikes in stock. How many bikes did she have originally?
There are approximately 4 weeks in a month.
The shop owner added 3 bikes every week for 4 weeks for a total addition of 3*4 = 
<gadget id="calculator">3*4</gadget>
<output>12</output>
12 bikes.
The shop owner now has the original number of bikes + 
<gadget id="calculator">12</gadget>
<output>12</output>
12 bikes.
She sold 18 bikes within the same time frame.
She now has a total of 45 bikes which is: the original number of bikes + 12 - 18 = 
<gadget id="calculator">45</gadget>
<output>45</output>
45 bikes.
The original number of bikes = 45-12+18 = 
<gadget id="calculator">45-12+18</gadget>
<output>51</output>
51 bikes.

<result>51</result>