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.

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?