Some years ago, the elder brother's current age was three times that of the younger brother's. The elder brother's age was the same as the younger brother's current age. The combined age of the elder brother and younger brother was 30 years old. Q: How old is your brother now? (solution by equation)
若干年前，哥哥现在的年龄是弟弟当年年龄的3倍，哥哥当年的年龄与弟弟现在的年龄相同，哥哥与弟弟现在的年龄和为30岁．问：哥哥现在多少岁？(用方程解)
<gadget id="calculator">30 + 30</gadget>
<output>60</output>

<gadget id="calculator">1 / 3</gadget>
<output>1/3 = around 0.333333</output>

<gadget id="calculator">1 + 1 + 1 + (1/3)</gadget>
<output>10/3 = around 3.333333</output>

<gadget id="calculator">60 / (10/3)</gadget>
<output>18</output>

<result>18</result>