Xiaohong saw a gray-haired old man, she asked him how old is he? The old man said: add 10 to my age and divide by 4, subtract 15 and multiply by 10, the result is exactly 100 years old. How old is this old man?
小红见到一位白发苍苍的老爷爷，她问老爷爷有多大年岁？老爷爷说：把我的年龄加上10用4除，减去15后用10乘，结果正好是100岁．请问这位老爷爷有多大年龄？
<gadget id="calculator">100 / 10</gadget>
<output>10</output>

<gadget id="calculator">10 + 15</gadget>
<output>25</output>

<gadget id="calculator">25 * 4</gadget>
<output>100</output>

<gadget id="calculator">100 - 10</gadget>
<output>90</output>

<result>90</result>