In the first seven months of this year, vegetable-growing households averaged 16 tons of vegetables per month in the first three months, and 19.5 tons of vegetables per month in the last four months. In the first seven months of this year, how many tons of vegetables are on the market every month?
种菜专业户在今年头七个月里，前3个月平均每月上市蔬菜16吨，后4个月平均每月上市蔬菜19.5吨．今年头七个月平均每月上市蔬菜多少吨？
<gadget id="calculator">16 * 3</gadget>
<output>48</output>

<gadget id="calculator">19.5 * 4</gadget>
<output>78</output>

<gadget id="calculator">48 + 78</gadget>
<output>126</output>

<gadget id="calculator">126 / 7</gadget>
<output>18</output>

<result>18</result>