A rectangular parallelepiped glass container is filled with water 15 cm deep, and a cube iron block with a side length of 6 cm is placed in it, and the water level rises by 3 cm. Then put in a cuboid iron block with a length of 6 cm, a width of 4.5 cm, and a height of 4 cm (the water has not overflowed). How many centimeters is the water depth now?
一个长方体玻璃容器，里面装有15厘米深的水，放入一块棱长6厘米的正方体铁块，水面上升3厘米．再放入一块长6厘米、宽4.5厘米、高4厘米的长方体铁块(水未溢出)，现在水深多少厘米？
<gadget id="calculator">6 / 3</gadget>
<output>2</output>

<gadget id="calculator">6 * 6 * 2</gadget>
<output>72</output>

<gadget id="calculator">4 / 72</gadget>
<output>1/18 = around 0.055556</output>

<gadget id="calculator">6 * 4.5 * (1/18)</gadget>
<output>1.5</output>

<gadget id="calculator">1.5 + 15 + 3</gadget>
<output>19.5</output>

<result>19.5</result>