Hi Mona,
Please refer the code snippet below to use onblur event in TextBox and the total value can be updated using javascript.
TextBox1 :
TextBox2 :
TextBox1 + TextBox2 :
Refer the sample below which illustrates the above.
http://files.syncfusion.com/support/GGC.Web/7.1.0.30/F80619/main.htmPlease let me know if this helps you.
Thanks,
Rekha