At the New Year's Gala, a total of 90 people participated in the performances of dancing, chorus and playing. If the number of people who only participate in dancing is three times the number of people who only participate in chorus; the number of people who participate in three programs at the same time is 7 less than those who only participate in chorus; 4 people; 50 people did not participate in the performance; 10 people participated in the dance and chorus but did not participate in the performance; 40 people participated in the chorus; then, how many people participated in the performance and chorus but did not participate in the dance.
新年联欢会上，共有90人参加了跳舞、合唱、演奏三种节目的演出．如果只参加跳舞的人数三倍于只参加合唱的人数；同时参加三种节目的人比只参加合唱的人少7人；只参加演奏的比同时参加演奏、跳舞但没有参加合唱的人多4人；50人没有参加演奏；10人同时参加了跳舞和合唱但没有参加演奏；40人参加了合唱；那么，同时参加了演奏、合唱但没有参加跳舞的有多少人．
<gadget id="calculator">50 - 10 - 10 - 10 - 3</gadget>
<output>17</output>

<result>17</result>