Visual C# MessageBox float

Question

I am trying to make a program with GUI that will design a heat exchanger. I am having some problems with MessageBox.Show, as it won't display the answer to some calculations. Any tips?

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

    private void textBox1_TextChanged(object sender, EventArgs e)
    {

    }

    private void button1_Click(object sender, EventArgs e)
    {
        float mc = float.Parse(textBox1.Text);
        mc = mc * (1000 / 3600);
        MessageBox.Show("mc=" + mc);
    }
}

PS: I am quite a newbie programmer, so don't be too harsh :D.