无法将类型'string'隐式转换为'decimal'

private void button18_Click(object sender, EventArgs e)
    {
        Form1 stForm = new Form1();
        DialogResult result = stForm.ShowDialog(this);

        if (result == DialogResult.Cancel)
            return;
        Inscrierea__pentru_burs_sau_contract media = new Inscrierea__pentru_burs_sau_contract();
        media.Media_MNDP = stForm.MNDP.Text;
        media.Media_MNEA = stForm.MNEA.Text;
        media.Media_Concurs = stForm.MediaConcurs.Text;

        db.Media.Add(media);
        db.SaveChanges();
        MessageBox.Show("Salvarea a avut loc cu succes!!!");
    }
private void button18_Click(object sender, Even