Some strange animals are gathering on the lawn. There are unipeds (1 head, 1 foot), double-headed dragons (2 heads, 4 legs), three-legged cats (1 head, 3 legs) and four-legged snakes (1 head, 4 legs). If the animals on the lawn have 58 heads and 160 feet, and the number of four-legged snakes is exactly twice that of two-headed dragons, how many unipeds are there?
一些奇异的动物在草坪上聚会．有独脚兽(1个头、1只脚)、双头龙(2个头、4只脚)、三脚猫(1个头、3只脚)和四脚蛇(1个头、4只脚)．如果草坪上的动物共有58个头、160只脚，且四脚蛇的数量恰好是双头龙的2倍，那么其中独脚兽有几只？
<gadget id="calculator">3 * 58</gadget>
<output>174</output>

<gadget id="calculator">174 - 160</gadget>
<output>14</output>

<gadget id="calculator">14 / 2</gadget>
<output>7</output>

<result>7</result>