Tax variable wont assign to new value (C)

Question

#include <stdio.h>

int main() {
    int inc;
    int ti;
    int tf;
    int n;
    int tax = 0;
    int const pd = 3600000;
    int const pa= 9000000;
    printf("Your income of this year: ");
    scanf("%ld", &inc);
    printf("\nNumber of dependent: ");
    scanf("%d", &n);
    tf = 12*(pa + n*pd);
    ti = inc - tf;
    printf("Tax-free income: %ld", tf);
    printf("\nTaxable income: %ld", ti);
    if (ti<= 0){
        printf("\nIncome tax: 0");
        return 0;
    }
    if (ti > 18000000){
        tax = (ti + 18000000) * (20 / 100);
        printf("\n %d %d \n", ti, tax);
        ti = 18000000;
    }
    if (ti > 10000001 && ti <=18000000){
        tax += (ti - 10000000) * (15 / 100);
        printf("%d %d \n", ti, tax);
        ti = 10000000;
    }
    if (ti > 5000001 && ti <=10000000){
        tax += (ti - 5000000) * (10 / 100);
        printf("%d %d \n", ti, tax);
        ti = 5000000;
    }
    if (ti <= 5000000){
        tax += ti * (5 / 100);
        printf("%d %d \n", ti, tax);
    }

    printf("\nIncome tax: %d", tax );
    return 0;
}

I can't get the tax variable to add up all the different value in my code. When debugging it keep printing out 0 for the tax variable. Sorry if I missed something important i am new student.