Use 25 small barrels and 12 large barrels to fill the water tank. Use 15 small barrels and 20 large barrels to fill the water tank. If you use 34 large barrels, the water tank will be full of 30 cubic decimeters. Find the volume of the vat.
用小桶25桶，大桶12桶可将水箱装满，改用小桶15桶，大桶20桶也可将水箱装满，如用大桶34桶，水箱的水就满出30立方分米．求大桶的容积．
<gadget id="calculator">25 / 5</gadget>
<output>5</output>

<gadget id="calculator">5 * 4</gadget>
<output>20</output>

<gadget id="calculator">20 + 12</gadget>
<output>32</output>

<gadget id="calculator">34 - 32</gadget>
<output>2</output>

<gadget id="calculator">30 / 2</gadget>
<output>15</output>

<result>15</result>