 Welcome to the session. I am Ashura and I am going to help you with the following position which says if A and B are two sets such that A is a subset of B then what is A union B? So first let us learn that A is a subset of B implies every element of A is an element of B. A union B is the set of all those X such that X belongs to either A or B or to both A and B. So this is the key idea we are going to use in this problem to find its solution. Let us now start with the solution and try to solve this problem with the help of Venn diagram. Let this circle denotes A and let us draw one more circle and circle in this circle and let it denote it by B. So the smaller circle denotes the set A and the bigger circle denotes the set B. Now observing we see that the set A is contained in set B and is A is a subset of B and all the elements which are in set A are also elements of set B. So union of A and B will be the whole circle B or the whole set B and thus we can say that A union B is equal to B. So our answer is B and this completes the solution. Hope you enjoyed it. Take care and have a good day.