Xiao Ming plans to spend a few days doing a set of exercises. If he does 5 questions a day, he can finish it by doing 10 questions a day in the last two days; if he does 6 questions a day, he can finish it one day in advance. Question: How many questions are there in this exercise set?
小明计划用若干天做一本习题集．如果他每天做5道题，那么最后两天每天要做10道题才能做完；如果他每天做6道题，恰好可以提前一天做完．请问：这本习题集中共有多少道题？
<gadget id="calculator">10 - 5</gadget>
<output>5</output>

<gadget id="calculator">2 * 5</gadget>
<output>10</output>

<gadget id="calculator">10 + 6</gadget>
<output>16</output>

<gadget id="calculator">6 - 5</gadget>
<output>1</output>

<gadget id="calculator">16 / 1</gadget>
<output>16</output>

<gadget id="calculator">16 - 2</gadget>
<output>14</output>

<gadget id="calculator">14 * 5</gadget>
<output>70</output>

<gadget id="calculator">10 * 2</gadget>
<output>20</output>

<gadget id="calculator">70 + 20</gadget>
<output>90</output>

<result>90</result>