A certain tree was 100 meters tall at the end of 2017. It will grow 10% more than its previous height each year. How long has the tree grown from 2017 until the end of 2019?
At the end of 2018, the tree will grow 100 x 10/100 = 
<gadget id="calculator">100*10/100</gadget>
<output>10</output>
10 meters more.
Thus, its height at the end of 2018 is 100 + 10 = 
<gadget id="calculator">100+10</gadget>
<output>110</output>
110 meters.
At the end of 2019, the tree will grow 110 x 10/100 = 
<gadget id="calculator">110*10/100</gadget>
<output>11</output>
11 meters more.
So, its height at the end of 2019 is 110 + 11 = 
<gadget id="calculator">110+11</gadget>
<output>121</output>
121 meters.
Therefore, the tree has grown 121 - 100 = 
<gadget id="calculator">121-100</gadget>
<output>21</output>
21 meters.

<result>21</result>