There are new bananas and oranges in the store, and the average number of boxes is 210. It is known that the number of boxes of oranges is twice that of bananas and 30 boxes less. How many boxes of bananas have you bought?
商店新进香蕉和橘子，平均箱数是210箱，已知橘子的箱数是香蕉的2倍少30箱，香蕉进了多少箱？
<gadget id="calculator">210 * 2</gadget>
<output>420</output>

<gadget id="calculator">30 + 420</gadget>
<output>450</output>

<gadget id="calculator">1 + 2</gadget>
<output>3</output>

<gadget id="calculator">450 / 3</gadget>
<output>150</output>

<result>150</result>