There are 20 questions in Xiaofu's Mathematical Olympiad test, 3 points for each question, and 2 points will be deducted for a wrong question or a missed answer. Xiaofu scored a total of 45 points. How many questions did he get right?
小福奥数考试，一共20题，每题3分，错一题或者不答一题倒扣2分，小福一共得了45分，他对了多少题．
<gadget id="calculator">20 * 3</gadget>
<output>60</output>

<gadget id="calculator">60 - 45</gadget>
<output>15</output>

<gadget id="calculator">3 + 2</gadget>
<output>5</output>

<gadget id="calculator">15 / 5</gadget>
<output>3</output>

<gadget id="calculator">20 - 3</gadget>
<output>17</output>

<result>17</result>