The ratio of the number of girls to boys participating in a certain oral English competition is 3:1. The average score of this competition is 84 points, and the average score of girls is 90 points. What is the average score of boys?
参加某次英语口语竞赛的女生人数和男生人数的比是3：1，这次竞赛的平均成绩是84分，其中女生的平均成绩是90分，男生的平均成绩是多少分
<gadget id="calculator">1 + 3</gadget>
<output>4</output>

<gadget id="calculator">84 * 4</gadget>
<output>336</output>

<gadget id="calculator">90 * 3</gadget>
<output>270</output>

<gadget id="calculator">336 - 270</gadget>
<output>66</output>

<gadget id="calculator">66 / 1</gadget>
<output>66</output>

<result>66</result>