The average of the three numbers A, B, and C is 20, and the sum of the numbers B and C is 25. What is the number of A?
甲、乙、丙三个数的平均数为20，乙、丙两数和为25，甲数为多少．
<gadget id="calculator">20 * 3</gadget>
<output>60</output>

<gadget id="calculator">60 - 25</gadget>
<output>35</output>

<result>35</result>