It is known that the ninth item of an arithmetic sequence is equal to 131, and the tenth item is equal to 137. What is the first item of this sequence? How much is item 19?
已知一个等差数列第9项等于131，第10项等于137，这个数列的第1项是多少？第19项是多少．
<gadget id="calculator">9 - 1</gadget>
<output>8</output>

<gadget id="calculator">137 - 131</gadget>
<output>6</output>

<gadget id="calculator">8 * 6</gadget>
<output>48</output>

<gadget id="calculator">131 - 48</gadget>
<output>83</output>

<gadget id="calculator">19 - 1</gadget>
<output>18</output>

<gadget id="calculator">18 * 6</gadget>
<output>108</output>

<gadget id="calculator">83 + 108</gadget>
<output>191</output>

<result>191</result>