A glass aquarium without a cover is 6 decimeters long, 3 decimeters wide, and 4.5 decimeters high. There is some water inside, the water surface is 3 decimeters high. What is the contact area between the glass of the fish tank and the water in square decimeters?
一个无盖的玻璃鱼缸，长6分米，宽3分米，高4.5分米．里面装有一些水，水面高3分米．现在鱼缸玻璃和水的接触面积是多少平方分米．
<gadget id="calculator">6 * 3</gadget>
<output>18</output>

<gadget id="calculator">3 * 3</gadget>
<output>9</output>

<gadget id="calculator">3 * 6</gadget>
<output>18</output>

<gadget id="calculator">18 + 9 + 18</gadget>
<output>45</output>

<gadget id="calculator">45 * 2</gadget>
<output>90</output>

<gadget id="calculator">90 - 18</gadget>
<output>72</output>

<result>72</result>