Need help with mortgage calculator

Question

Sorry if this has been posted before but I searched the forum and couldn't find a solution. Basically, I need to create a mortgage calculator in C# that allows the user to input the mortgage amount, the interest rate and the duration of the mortgage, the program has to contain a button which, when pressed, calculates the interest the user has to pay, calculates the total amount the user has to pay and the monthly repayments. Below is a copy of the code I've written so far, I was told to use an integer instead of a float/double by my teacher, who said its more efficient. However, there's an error, as when i run the program and type in all of the text boxes and click on the button the outputs are messed up. If someone could take a look at the code and see what I've done wrong and correct it for me I would really appreciate it. Thanks

        public int Amount;

        public int InterestRate;

        public int LoanDuration;

        public int InterestToBePaid;

        public int TotalAmountToBePaid;

        public int MonthlyRepayments;

        public frmMortgageCalculator()

        {

            InitializeComponent();

        }

        private void tabpSimpleInterest_Click(object sender, EventArgs e)

        {

        }

        private void btnCalculate_Click(object sender, EventArgs e)

        {

            try

            {

                Amount = int.Parse(txtAmount.Text);

                InterestRate = int.Parse(txtInterestRate.Text);

                LoanDuration = int.Parse(txtDuration.Text);

                //Calculates the interest

                InterestToBePaid = InterestRate / 100 * Amount;

                lblInterestToBePaid.Text = "The Total Interest You Have To Pay Is:" + InterestToBePaid;

                // Calculates the total amount

                TotalAmountToBePaid = Amount + InterestRate;

                lblTotalAmountToBePaid.Text = "The Total Amount You Have To Pay Is:" + TotalAmountToBePaid;

                //Calculates the monthly repayments 

                MonthlyRepayments = Amount + InterestRate / LoanDuration;

                lblMonthlyRepayments.Text = "Your Monthly Repayments Are:" + MonthlyRepayments;

            }

            catch(Exception exc)

            {

                MessageBox.Show(exc.Message);

            }