ship sails downstream from Pier A to Pier B, and then goes back to Pier C for 20 hours. It is known that the speed of the ship in still water is 7.5 km/h, and the speed of the current is 2.5 km/h. If the distance between A and C is 40 km shorter than the distance between A and B, find the distance between A and B.
某船从A码头顺流航行到B码头，然后逆流返行到C码头，共行20小时，已知船在静水中的速度为7.5千米/时，水流的速度为2.5千米/时，若A与C的距离比A与B的距离短40千米，求A与B的距离．
<gadget id="calculator">7.5 + 2.5</gadget>
<output>10</output>

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

<gadget id="calculator">1 / 3</gadget>
<output>1/3 = around 0.333333</output>

<gadget id="calculator">10 * 20 * (1/3)</gadget>
<output>200/3 = around 66.666667</output>

<result>200/3 = around 66.666667</result>