Pairwise coding problem

I am having problem in this question.I dont know how to approachTell us what’s happening:

Your code so far

function pairwise(arr, arg) {
  return arg;
}

pairwise([1,4,2,3,0,5], 7);

Your browser information:

Your Browser User Agent is: Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/65.0.3325.181 Safari/537.36.

Link to the challenge:
https://www.freecodecamp.org/challenges/pairwise

Are you able to do the following?

var arr = [1,4,2,3,0,5];

// Using the given array, arr, generate the pairwise sums of the first number
// in the array with each of the rest of the numbers in the array, that is:
// 1 + 4 = 5;
// 1 + 2 = 3;
// 1 + 3 = 4;
// ... etc.

I am having problem in solving the question

Do you understand what the challenge is asking your function to do? Do you understand the example they give in the challenge instructions (seen below)?

For example pairwise([7, 9, 11, 13, 15], 20) returns 6. The pairs that sum to 20 are [7, 13] and [9, 11].

Do you understand why the function should return 6 for the above function call?