课后，小林查到光从玻璃射向空气时的一些数据如下表：

表中数据说明：

下图为水循环模式图，I为区域外水汽输入量，P为总降水量，E为区域内蒸发量，O为从区域输出的水汽总量，R₁为流入区域的径流量，R₂为流出区域的径流量，W为空中水汽含量。据此完成下列各题。

根据短文内容,回答下列问题。
   This is my story. I’m French. I fly planes in Africa.
   One day, when I was flying a very small plane, there was something wrong with the engine(发动机).The engine stopped. The plane was light and I could land it safely on the ground.
   Where was I? I couldn’t see any houses or farms. I had a bottle of water and two oranges. I had a map, too. The first day, I didn’t eat anything. In the evening, I began walking. When the sun went down, the air got cold. Where should I walk? I looked at my map and the moon and the stars. I walked and walked.
   The sun came up on the morning of the second day. It was too hot to walk. In the evening, I began walk. I ate an orange and drank a little water.
   The third day, I ate the second orange. The bottle of water was now empty. There were no houses, no trees, and no water.
   The hot sun came up on the fourth day. Would this be the last day on the earth? I didn’t know. What was that? A bird? A man on a hill? No! Yes, it was! I walked to him excitedly and said hello to him. He looked at me and then gave me some water. I drank and drank...

已知菱形的两条对角线长分别为2cm，3cm，则它的面积是____ cm²．