The water surface area of West Lake used to be 5.6 square kilometers, but it increased to 6.5 square kilometers after treatment. How many hectares has the water surface area of West Lake increased?
西湖水面面积原来5.6平方千米，治理后增加到6.5平方千米，西湖水面面积增加了多少公顷．
<gadget id="calculator">6.5 - 5.6</gadget>
<output>0.9</output>

<gadget id="calculator">0.9 * 100</gadget>
<output>90</output>

<result>90</result>