The packaging of a medicine bottle reads: 90 tablets, each 10 mg. The prescription written by the doctor reads: eat 3 times a day, 20 mg each time. How many days can this bottle of medicine be taken according to the doctor's prescription?
一种药瓶的包装上写着：90片，每片10毫克．医生开的处方上写着：每天吃3次，每次20毫克．这瓶药按医生的处方，可以吃多少天？
<gadget id="calculator">20 / 10</gadget>
<output>2</output>

<gadget id="calculator">2 * 3</gadget>
<output>6</output>

<gadget id="calculator">90 / 6</gadget>
<output>15</output>

<result>15</result>