First take asynch BPEL to perform addtion

Modify the inputs as two in XSD level

]

Take assign activity and perform addition, assign the result to output.

]

Deploy it and test the project in EM console

This project wont give the output as it is asynch processs.

Copy the WSDL URL

Take a new project in that take synch BPEL

Modify the inputs as two in XSD level

Create a Webservice On right side i.e reference side

Paste the WSDL URL

Give port type ,callback port type

Take invoke activity and connect to the Webservice

Create a invoke variable

Take assign and assign the inputs to invoke inputs

Take Receive Activity and connect to Webservice

Create a Receive variable

Take assign activity and assign receive variable to output variable

Deploy it

Test the project in EM console

This time you will get the result.