A ship travels back and forth between two piers. The speed along the current is 12km/h faster than the speed against the current. It takes a total of 6 hours. It is known that the first three hours travel 30km more than the last three hours. How many kilometers is the whole journey?
一艘船在两个码头之间往返一个来回，顺水速度比逆水速度快12km/h，一共6小时，已知前三小时比后三小时多走30km，求全程是多少千米？
<gadget id="calculator">30 / 12</gadget>
<output>5/2 = around 2.5</output>

<gadget id="calculator">6 - (5/2)</gadget>
<output>7/2 = around 3.5</output>

<gadget id="calculator">(7/2) - (5/2)</gadget>
<output>1</output>

<gadget id="calculator">30 / 1</gadget>
<output>30</output>

<gadget id="calculator">30 * (7/2)</gadget>
<output>105</output>

<result>105</result>