Fangfang’s family used 13.2 tons of water in April, which is 1.8 tons less than last month. How many tons did Fangfang’s family use last month?
芳芳家四月份用水13.2吨，比上个月节约了1.8吨，芳芳家上个月用水多少吨？
<gadget id="calculator">13.2 + 1.8</gadget>
<output>15</output>

<result>15</result>