https://hyperskill.org/learn/step/3795

solve.java

import java.util.*;

public class Main {

  public static void main(String[] args) {
    Scanner scanner = new Scanner(System.in);
    int companyNum = scanner.nextInt();

    List<Integer> incomes = new ArrayList<>();
    List<Integer> taxPer = new ArrayList<>();

    for (int i = 0; i < companyNum; i++) {
      incomes.add(scanner.nextInt());
    }

    for (int i = 0; i < companyNum; i++) {
      taxPer.add(scanner.nextInt());
    }

    int mostPayedCompanyIndex = 0;
    int maxPayedTax = 0;
    for (int i = 0; i < incomes.size(); i++) {
      int tax = getPayedTax(incomes.get(i), taxPer.get(i));
      if (maxPayedTax < tax) {
        mostPayedCompanyIndex = i;
        maxPayedTax = tax;
      }
    }
    System.out.println(mostPayedCompanyIndex + 1);
  }

  private static int getPayedTax(int income, int taxPer) {
    return income * taxPer;
  }
}