The school carried out water saving activities. A total of 14.7 tons of water was saved in the first 3 days of this week, and 4.2 tons of water was saved every day in the next 4 days. How many tons of water was saved on average this week?
学校开展节约用水活动，这星期前3天共节约用水14.7吨，后4天每天节约用水4.2吨，这星期平均每天节约用水多少吨？
<gadget id="calculator">4.2 * 4</gadget>
<output>16.8</output>

<gadget id="calculator">14.7 + 16.8</gadget>
<output>31.5</output>

<gadget id="calculator">4 + 3</gadget>
<output>7</output>

<gadget id="calculator">31.5 / 7</gadget>
<output>4.5</output>

<result>4.5</result>