Calling two web service methods

Hi All, I am new to soapUI tool.
In my application two web service method are there.
I want to test by calling one after another one.

For Example:

add(5,5) output is 10.

I want test like this:

call add(5,5);
if (add(5,5) == 10) {
call add(6,5)
if (add(6,5) !=10) {
call sub(7,5);
} else {
call sub(7,5);
}
How to implement this code in assertion for testing. Please guide asap....