After a sea turtle is born, its weight increases by an average of 100 grams per year. After 40 years, its weight will increase to 4080 grams. Do you know how many grams a sea turtle weighs when it is just born?
海龟出生后，体重平均每年增加100克，40年后它的体重将增加到4080克，你知道海龟刚出生时有多少克吗？
<gadget id="calculator">100 * 40</gadget>
<output>4_000</output>

<gadget id="calculator">4_080 - 4_000</gadget>
<output>80</output>

<result>80</result>