Step 1 :Given that the number of elements in set A, denoted as \(n(A)\), is 20.
Step 2 :Given that the number of elements in set B, denoted as \(n(B)\), is 60.
Step 3 :Given that the number of elements in the intersection of set A and set B, denoted as \(n(A \cap B)\), is 15.
Step 4 :Given that the number of elements in the universal set U, denoted as \(n(U)\), is 200.
Step 5 :The number of elements in the subset that is not in A and not in B, denoted as \(n(A^{\prime} \cap B^{\prime})\), can be found by subtracting the number of elements in A, B and the intersection of A and B from the total number of elements in the universal set U.
Step 6 :So, \(n(A^{\prime} \cap B^{\prime}) = n(U) - n(A) - n(B) + n(A \cap B)\).
Step 7 :Substitute the given values into the equation, we get \(n(A^{\prime} \cap B^{\prime}) = 200 - 20 - 60 + 15\).
Step 8 :Simplify the equation, we get \(n(A^{\prime} \cap B^{\prime}) = 135\).
Step 9 :Final Answer: The number of elements in the subset that is not in A and not in B is \(\boxed{135}\).