A steamship goes down the river, traveling 120 kilometers per hour in the first 3 hours, and a total of 90 kilometers in the next 3 hours. How many kilometers per hour does the ship travel on average?
一首轮船顺流而下，前3小时每小时行120千米，后3小时共行驶90千米，这艘轮船平均每小时行驶多少千米？
<gadget id="calculator">120 * 3</gadget>
<output>360</output>

<gadget id="calculator">360 + 90</gadget>
<output>450</output>

<gadget id="calculator">3 + 3</gadget>
<output>6</output>

<gadget id="calculator">450 / 6</gadget>
<output>75</output>

<result>75</result>