Calculate tax amount based on TextBox value using C# in ASP.Net

I want to calculate the service tax on some amount. The value of service tax must be taken from textbox1.text and amount from textbox2.text and then after calculating it must be store in another textbox say,textbox3.text

service tax = textbox1.text - 14.5% amount = textbox2.text - 44000 total amount= textbox3.text -((14.5*44000)/100 )+ 44000 ;

The Value of ((14.5*44000)/100 )+ 44000 after calculating will be store in textbox3.text

How Can i achieve this task please give me the solution..