The ratio of heartbeats per minute between adults and children is 7:9, children's heartbeats are about 90 beats per minute, and adults' heartbeats are about how many times per minute.
成年人和儿童每分钟心跳次数的比是7：9，儿童每分钟心跳90次左右，成年人每分钟心跳约多少次．
<gadget id="calculator">9 / 7</gadget>
<output>9/7 = around 1.285714</output>

<gadget id="calculator">90 / (9/7)</gadget>
<output>70</output>

<result>70</result>