A ship goes down the river, traveling 40 kilometers per hour in the first 3 hours, and a total of 90 kilometers in the next 4 hours. How many kilometers per hour does the ship travel on average?
一艘轮船顺流而下，前3个小时每小时行40千米，后4个小时共行驶90千米，这艘轮船平均每小时行使多少千米？
<gadget id="calculator">40 * 3</gadget>
<output>120</output>

<gadget id="calculator">120 + 90</gadget>
<output>210</output>

<gadget id="calculator">3 + 4</gadget>
<output>7</output>

<gadget id="calculator">210 / 7</gadget>
<output>30</output>

<result>30</result>