The distance between AB and AB is 20 kilometers. Three people A, B, and C start from A at the same time. When A arrives at B, B and C are 4 kilometers and 5 kilometers away from B respectively. When B arrives at B, how far is C from B?
AB两地相距20千米，A、B、C三个人同时从A地出发，A到达B地的时候，B、C分别距B地为4千米和5千米．B到达B地的时候，C距离B地还有多少米．
<gadget id="calculator">20 - 4</gadget>
<output>16</output>

<gadget id="calculator">20 - 5</gadget>
<output>15</output>

<gadget id="calculator">16 / 15</gadget>
<output>16/15 = around 1.066667</output>

<gadget id="calculator">1 / (16/15)</gadget>
<output>15/16 = around 0.9375</output>

<gadget id="calculator">20 * (15/16)</gadget>
<output>75/4 = around 18.75</output>

<gadget id="calculator">20 - (75/4)</gadget>
<output>5/4 = around 1.25</output>

<gadget id="calculator">(5/4) * 1_000</gadget>
<output>1_250</output>

<result>1_250</result>