Three-quarters of the oil from a 4000-liter tank (that was initially full) was poured into a 20000-liter capacity tanker that already had 3000 liters of oil. How many more liters of oil would be needed to make the large tanker half-full?
Three-quarters of oil from the initially full 4000-liter tank would be 4000*(3/4)= 
<gadget id="calculator">4000*3/4</gadget>
<output>3_000</output>
3000 liters.
In addition to the 3000 liters that were already in the large tanker, there are 3000+3000 = 
<gadget id="calculator">3000+3000</gadget>
<output>6_000</output>
6000 liters in it now.
The tanker would be filled to half capacity by (1/2)*20000 = 
<gadget id="calculator">(1/2)*20000</gadget>
<output>10_000</output>
10000 liters of oil.
There are 10000-6000 = 
<gadget id="calculator">10000-6000</gadget>
<output>4_000</output>
4000 liters left to reach half capacity.

<result>4_000</result>