For a nine-digit number, a is in the billion digit, b is in the tens of thousands digit, and c is in the ones digit. a is 4 times larger than b, and b is 5 times larger than c. The rest of you are all 0. What is this number?
一个九位数，亿位上是a，万位上是b，个位上是c．a比b大4，b是c的5倍．其余各位上都是0．这个数是多少．
<result>900_050_001</result>