There are two big and small circles. The sum of their areas is 1991 square centimeters. The circumference of the small circle is (9/10) that of the large circle. What is the area of the large circle?
有大、小两个圆，它们的面积之和是1991平方厘米，小圆的周长是大圆的(9/10)，求大圆的面积是多少？
<gadget id="calculator">81 / 100</gadget>
<output>81/100 = around 0.81</output>

<gadget id="calculator">1 + (81/100)</gadget>
<output>181/100 = around 1.81</output>

<gadget id="calculator">1_991 / (181/100)</gadget>
<output>1_100</output>

<result>1_100</result>