Liu Xiaofang measured the temperature last Saturday morning at 21.5°C. At noon, the temperature was 3.6°C higher than in the morning, and at night it was 4.5°C lower than at noon. What is the temperature at night?
刘小芳上周六早上量得气温是21.5℃，中午气温比早上升高了3.6℃，晚上比中午降低了4.5℃，晚上的气温是多少？
<gadget id="calculator">3.6 - 4.5</gadget>
<output>-0.9</output>

<gadget id="calculator">21.5 + (-0.9)</gadget>
<output>20.6</output>

<result>20.6</result>