Answer:

Let the the set is S={a,b,c,d} and it is given that a+d=15.

Now fisrt choose the smallest number in the given set of 13 integers.It

is 2 and according to 2 the largest number is 15−2=13. Now fix 2 and 13 in the

place of a and d.Now we have S={2,b,c,13} and now choose b,c from the residue

set (besides 14){3,4,5,6,7,8,9,10,11,12}. The total number of ways doing this ⟹(102).The

strategy is to choose the minimum and accordingly maximum will be chosen.Then

Count the number of ways from the residue set={minimum,...,maximum}.Then add

them for each minimum or maximum case, then you will have the answer of your

required question.

Step-by-step explanation:

carry on heheh