Each large-character book has 15 sheets, and each sheet of paper can write 20 large characters. Xiao Ming writes 6 more sheets to fill them all. How many large characters has Xiao Ming written?
大字本每本15张，每张纸可写20个大字，小明再写6张就全部写满，小明已经写了多少个大字？
<gadget id="calculator">15 - 6</gadget>
<output>9</output>

<gadget id="calculator">9 * 20</gadget>
<output>180</output>

<result>180</result>