Grandpa Wang spent 870 yuan to wholesale 29 boxes of apples. After he sold 21 boxes at a price of 35 yuan per box, he sold the rest at a reduced price. Grandpa Wang made a total of 89 yuan. How much did the rest sell for each box?
王爷爷花870元批发了29箱苹果，他以每箱35元的价格卖出21箱后，余下的降价卖出．王爷爷一共赚了89元，余下的每箱卖了多少元？
<gadget id="calculator">870 / 29</gadget>
<output>30</output>

<gadget id="calculator">35 - 30</gadget>
<output>5</output>

<gadget id="calculator">5 * 21</gadget>
<output>105</output>

<gadget id="calculator">105 - 89</gadget>
<output>16</output>

<gadget id="calculator">29 - 21</gadget>
<output>8</output>

<gadget id="calculator">16 / 8</gadget>
<output>2</output>

<gadget id="calculator">30 - 2</gadget>
<output>28</output>

<result>28</result>