The sum of the three numbers A, B, and C is 300. It is known that the number A is 50 greater than the number B, and the number B is 20 greater than the number C. What is the number A?
甲、乙、丙三个数之和为300，已知甲数比乙数大50，乙数比丙数大20，甲数是多少？
<gadget id="calculator">50 + 20</gadget>
<output>70</output>

<gadget id="calculator">300 + 50 + 70</gadget>
<output>420</output>

<gadget id="calculator">420 / 3</gadget>
<output>140</output>

<result>140</result>