How to see if object is contained in an embedded NSArray, then grab the other items in the set

How to see if object is contained in an embedded NSArray, then grab the
other items in the set

I currently have a NSArray which contains many NSArrays, each containing a
pair of NSStrings such like the following: [["A", "B"], ["U", "A"], ["X",
"Y"], ...], and I am interested first checking to see if it contains a
particular object, and then grabbing the other paired object and putting
it in an array. For example, if I am checking for "A" in the above array,
the result array would contain ["B", "U"]
I know how to iterate over each array, but am trouble deciding how to grab
the paired object inside the array... thanks!
for (NSArray *innerArray in outerArray){
if ([innerArray containsObject: @"A"]){
//how to extract the other object and save it to an array?
}
}