A hunting dog found a running rabbit 7 steps away from it, and immediately chased after it. It is known that the hunting dog runs 4 steps and the rabbit runs 10 steps. The rabbit moves fast, and the dog runs 10 steps. The hunting dog can only run 6 steps. How many steps must the hound run to catch up with the rabbit?
一只猎狗发现在离它7步远的前方有一只正在奔跑的小兔，就立刻追上去．已知猎狗跑4步小兔跑10步，小兔动作快，它跑10步猎狗只能跑6步．猎狗至少跑出多少步才能追上小兔？
<gadget id="calculator">5 / 5</gadget>
<output>1</output>

<gadget id="calculator">2 / 3</gadget>
<output>2/3 = around 0.666667</output>

<gadget id="calculator">1 / (2/3)</gadget>
<output>3/2 = around 1.5</output>

<gadget id="calculator">1 / (3/2)</gadget>
<output>2/3 = around 0.666667</output>

<gadget id="calculator">1 - (2/3)</gadget>
<output>1/3 = around 0.333333</output>

<gadget id="calculator">7 / (1/3)</gadget>
<output>21</output>

<result>21</result>