The average lifespan of a sea lion is (3/4) that of a walrus, the average lifespan of a seal is (1/2) that of a walrus, and the average lifespan of a sea lion is 10 years longer than that of a seal, so the average lifespan of a seal is How old is it?
海狮的平均寿命是海象的平均寿命的(3/4)，海豹的平均寿命是海象的平均寿命的(1/2)，海狮的平均寿命比海豹的平均寿命多10岁，则海豹的平均寿命为多少岁．
<gadget id="calculator">3 / 4</gadget>
<output>3/4 = around 0.75</output>

<gadget id="calculator">1 / 2</gadget>
<output>1/2 = around 0.5</output>

<gadget id="calculator">(3/4) - (1/2)</gadget>
<output>1/4 = around 0.25</output>

<gadget id="calculator">10 / (1/4)</gadget>
<output>40</output>

<gadget id="calculator">40 * (1/2)</gadget>
<output>20</output>

<result>20</result>