There is a certain amount of money in Dad's mobile phone card. If he spends 6 yuan a day, he can use it for 18 days. If you save 1.5 yuan per day, how many days can this stored-value card be used for?
爸爸的手机卡中有一定数额的钱，如果每天消费6元，能使用18天．如果每天节约1.5元，这张储值卡可以使用多少天？
<gadget id="calculator">6 - 1.5</gadget>
<output>4.5</output>

<gadget id="calculator">18 / 4.5</gadget>
<output>4</output>

<gadget id="calculator">6 * 4</gadget>
<output>24</output>

<result>24</result>