John buys 30 ducks for $10 each.  They weigh 4 pounds and he sells them for $5 per pound.  How much profit did he make?
He bought the ducks for 30*10=$
<gadget id="calculator">30*10</gadget>
<output>300</output>
300.
He sold each duck for 4*5=$
<gadget id="calculator">4*5</gadget>
<output>20</output>
20.
So he sold all the ducks for 30*20=$
<gadget id="calculator">30*20</gadget>
<output>600</output>
600.
So he made a profit of 600-300=$
<gadget id="calculator">600-300</gadget>
<output>300</output>
300.

<result>300</result>