Problem 8 [Java]

Hi, I do not understand, why the server does not consider the right my decision:

import java.util.Scanner;

class Main {
    public static void main(String[] args) {
        Scanner scn = new Scanner(System.in);
        int a = scn.nextInt();
        for (int i = 0; i < a; i++) {
            int b = scn.nextInt();
            int c = scn.nextInt();
            int d = scn.nextInt();
            System.out.println(((2*b + c * (d - 1)) / 2) * d + " ");
        }
    }
}

My decision is based on this formula: