ComboBox Simplifying Method

I have 3 or more ComboBoxes having the same functionality. what I'm thinking is creating a Method and just call it

Here is sample code

Question: Is there any way to Combine this 5 ComboBox into 1 since they have the same functionality and simplify this Method if for example i'm having multiple ComboBoxes

    public double comboBoxTry()
    { double x;
    if (comboBox1.SelectedItem.ToString() == "First")
    { x = 3.5; }
    else if (comboBox1.SelectedItem.ToString() == "Second")
    { x = 4; }

    //Second ComboBox and so on
    if (comboBox2.SelectedItem.ToString() == "First")
    { x = 3.5; }
    else if (comboBox2.SelectedItem.ToString() == "Second")
    { x = 4; }

if (comboBox2.SelectedItem.ToString() == "First")
    { x = 3.5; }
    else if (comboBox2.SelectedItem.ToString() == "Second")
    { x = 4; }

if (comboBox3.SelectedItem.ToString() == "First")
    { x = 3.5; }
    else if (comboBox3.SelectedItem.ToString() == "Second")
    { x = 4; }

if (comboBox4.SelectedItem.ToString() == "First")
    { x = 3.5; }
    else if (comboBox4.SelectedItem.ToString() == "Second")
    { x = 4; }


if (comboBox5.SelectedItem.ToString() == "First")
    { x = 3.5; }
    else if (comboBox5.SelectedItem.ToString() == "Second")
    { x = 4; }

// I want to Combine this  5 ComboBox  into 1 since  they have the same functionality 

    return x;
    }

    private void btnCompute_Click(object sender, EventArgs e)
        { txtResult.Text = (x * double.Parse(txtAmount.Text)).ToString(); }