Xiaohua's average score for the three subjects outside Chinese and Mathematics is 85, of which Chinese and foreign languages are 90 and 78 respectively. What is his math score?
小花的语数外三门功课平均成绩是85分，其中语文、外语分别是90，78，他的数学成绩是多少．
<gadget id="calculator">85 * 3</gadget>
<output>255</output>

<gadget id="calculator">255 - 90 - 78</gadget>
<output>87</output>

<result>87</result>