A vegetable field harvested 15 tons of cabbage this year, an increase of 20% compared to last year. How many tons of cabbage was harvested in this vegetable field last year?
一块菜地，今年收白菜15吨，比去年增产20%，去年这块菜地收白菜多少吨？
<gadget id="calculator">20 / 100</gadget>
<output>1/5 = around 0.2</output>

<gadget id="calculator">1 + (1/5)</gadget>
<output>6/5 = around 1.2</output>

<gadget id="calculator">15 / (6/5)</gadget>
<output>25/2 = around 12.5</output>

<result>25/2 = around 12.5</result>