关于PTA的问题，如何解决？

Question

问题遇到的现象和发生背景

问题相关代码，请勿粘贴截图

函数接口定义：

double m_tax(double salary,int month);//计算每月累计应纳税额

函数返回每月累计应纳税额;
裁判测试程序样例：

#include<stdio.h>

double m_tax(double salary,int month);

int main()
{
    double money,tax,sum=0;
    int i;
    for(i=1;i<=12;i++)
    {
        scanf("%lf",&money);
        sum+=money;
        tax=m_tax(money,i);
        printf("the sum of %d months tax is %.2f\n",i,tax);
    }
    return 0;
}
/* 请在这里填写答案 */

我想要达到的结果

Answer 1

double sum=0;
double m_tax(double salary,int month)
{
    double s,tax;
    sum+=salary;
    if(sum<=month*5000)
        tax=0;
    else
    {
        s=sum-month*5000;
        if(s<=36000)
            tax=s*0.03;
        else if(s<=144000)
            tax=s*0.1-2520;
        else if(s<=300000)
            tax=s*0.2-16910;
        else if(s<=420000)
            tax=s*0.25-31920;
        else if(s<=660000)
            tax=s*0.30-52920;
        else if(s<=960000)
            tax=s*0.35-85920;
        else
            tax=sum*0.45-181920;
    }
    return tax;
}