Write down all elements of ({9, 10, 11} ∩ {10, 11, 12, 13}) ∪ {14, 15}. (enter your answer in set notation.)

What we have so far:
Let set A = {9, 10, 11}
Let set B = {10, 11, 12, 13}
Let set C = A∩B. This means: the intersection of A & B.
Let set D = {14, 15}
Let set Universal = C∪D. This means: the union of C & D where C is the intersection of A & B.

Solution:
Let us first solve for set C.
C = A∩B
C = {9, 10, 11} ∩ {10, 11, 12, 13}
C = {10, 11} <--- New value for set C

Let us now solve for set Universal.
Universal =  C∪D
Unviversal =  {10, 11} ∪ {14, 15}
∴ Universal = {10, 11, 14, 15} <--- What we are looking for.

Therefore, the answer is Universal = {10, 11, 14, 15}.