How to add the value of the two text boxes in the 3rd text box in ssrs table?

Hi ,

in my ssrs table i encountered a situation where i need to computing for the two text box values and i have to show that value in page header.

for example i have to add the textbox9 value and textbox12 value then i have to show that value in the page header.

Please help me with this requirement.

Thanks in advance,

Naveen