There are 4 trains waiting at a train station and each train has 4 carriages. Each carriage has 3 rows of wheels and the rows of wheels have 5 wheels each. How many wheels are at the train station?
Each carriage has 3 rows of wheels * 5 wheels per row = 
<gadget id="calculator">3*5</gadget>
<output>15</output>
15 wheels.
So each train has 4 carriages * 15 wheels per carriage = 
<gadget id="calculator">4*15</gadget>
<output>60</output>
60 wheels.
There is therefore a total of 4 trains * 60 wheels per train = 
<gadget id="calculator">4*60</gadget>
<output>240</output>
240 wheels at the train station.

<result>240</result>