calculating grand total for the script having many fields

hi experts,

currently working on the script related to SD.i want to display the grand total for the four fields which are having as follow.every field is having two items value.i calculated subtotals of each field but when i am trying calculate the grand total for the four fields it is not giving the result even though i tried to calculate the grand total by the usual way.help

EXBED EXSED EXAED CESS ECS

item 1 value

item 2 value

grand total : (sub total of EXBED , EXSED , EXAED , CESS , ECS)