In a parking lot, there are 48 cars and motorcycles parked. Each car has 4 wheels, and each motorcycle has 3 wheels. These cars have 172 wheels in total. How many motorcycles are there in the parking lot?
在一个停车场上，汽车、摩托车共停了48辆，其中每辆汽车有4个轮子，每辆摩托车有3个轮子，这些车共172个轮子，停车场上有摩托车多少辆．
<gadget id="calculator">48 * 4</gadget>
<output>192</output>

<gadget id="calculator">192 - 172</gadget>
<output>20</output>

<gadget id="calculator">4 - 3</gadget>
<output>1</output>

<gadget id="calculator">20 / 1</gadget>
<output>20</output>

<result>20</result>