The tractor factory plans to manufacture 720 tractors. It has been working for 4.5 days, with an average of 90 tractors per day. The rest will be completed within 3 days. How many tractors are manufactured per day on average?
拖拉机厂计划制造720台拖拉机，已经干了4.5天，平均每天制造90台，剩下的要在3天内完成，平均每天制造多少台？
<gadget id="calculator">90 * 4.5</gadget>
<output>405</output>

<gadget id="calculator">720 - 405</gadget>
<output>315</output>

<gadget id="calculator">315 / 3</gadget>
<output>105</output>

<result>105</result>