There are 18 people taking a group photo, the price is 6 yuan for 3 pieces, plus 1 yuan for each picture. If each person needs one, how much is the total payment?
有18人合影照相，价格是3张6元，另外加洗每张1元．如果每人需要1张，共付多多少元？
<gadget id="calculator">18 - 3</gadget>
<output>15</output>

<gadget id="calculator">15 * 1</gadget>
<output>15</output>

<gadget id="calculator">6 + 15</gadget>
<output>21</output>

<result>21</result>