Buy A and B stamps 13 pieces, each type A stamp is 4 yuan, each type B stamp is 2 yuan, a total of 40 yuan. How many stamps of type A to buy?
买甲，乙两种邮票13张，甲种邮票每张4元，乙种邮票每张2元，一共用40元．甲种邮票买多少张．
<gadget id="calculator">13 * 2</gadget>
<output>26</output>

<gadget id="calculator">40 - 26</gadget>
<output>14</output>

<gadget id="calculator">4 - 2</gadget>
<output>2</output>

<gadget id="calculator">14 / 2</gadget>
<output>7</output>

<result>7</result>