To pave a classroom, it takes 450 square bricks with a side length of 20 cm. If the square bricks with a side length of 30 cm are used instead, how many bricks are needed? (Solve with ratio)
铺一间教室，用边长20厘米的方砖需要450块，如果改用边长30cm的方砖，需要多少块？(用比例解)
<gadget id="calculator">20 * 20 * 450</gadget>
<output>180_000</output>

<gadget id="calculator">30 * 30</gadget>
<output>900</output>

<gadget id="calculator">180_000 / 900</gadget>
<output>200</output>

<result>200</result>