Sir !
thank you , you are the best!
I got it by my self and it very easy!

Code:
            Dim Target = txtTarget.Text * 6     'declare var Target assign value from txttarget * 6
            Dim Efficiency = total_Input / Target       'compute eff by dividing t_input /target
            txtEfficiency.Text = Efficiency.ToString("p2")  'p2 * 100 and percent sign
            txtTotalInputEff.Text = total_Input.ToString