---

Говорит и пишет на экономическом языке. Да здравствует

using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Data;
using System.Drawing;
using System.Linq;
using System.Runtime.InteropServices;
using System.Text;
using System.Threading.Tasks;
using System.Windows.Forms;

namespace WindowsFormsApp2
{
    public partial class Form1: Form
    {
        public Form1()
        {
            InitializeComponent();
        }

        private void label2_Click(object sender, EventArgs e)
        {

        }

        private void button1_Click(object sender, EventArgs e)
        {
            int price = 0;
            if (comboBox2.Text == "92")
            {
                price = 70;
            } else if (comboBox2.Text == "95")
            {
                price = 73;
            } else if (comboBox2.Text == "ДТ")
            {
                price = 80;
            } else
            {
                label3.Text = "Выберите тип полива";
                return;
            }

            double money;

            double.TryParse(textBox1.Text, out money);

            if (money <= 0)
            {
                label3.Text = "У вас недостаточно денег";
                return;
            }

            double litters = money / price;
            double change = money % price;

            label3.Text = $"Вы получите {litters:F2} литров и {change:F2} сдачей";
        }

        private void textBox1_TextChanged(object sender, EventArgs e)
        {
     
        }

        private void label3_Click(object sender, EventArgs e)
        {

        }
    }
}