Conditional sum with infopath form

Hello All
To get the conditional sum in repeating table (which acts like gridview)
as follows


1)Set the property of repeating table as given following image




Add textbox(field2) to the row of repeating table and other textbox(field4) to the footer
of table and checkbox as shown in the fig

right click on the properties of textbox-->change the default value by clicking on fx
--insert function-->select sum-> insert field-->select the field-->click on the filter button-->select the checkbox value is equal to true

as shown