It is known that the first item of the arithmetic sequence is 5, and the eighth item is 26. What is the tolerance of this arithmetic sequence.
已知等差数列首项是5，第8项是26，这个等差数列的公差是多少．
<gadget id="calculator">26 - 5</gadget>
<output>21</output>

<gadget id="calculator">8 - 1</gadget>
<output>7</output>

<gadget id="calculator">21 / 7</gadget>
<output>3</output>

<result>3</result>