What rule shows the input and output of the reflection

Trapezoid ABCD is reflected over the line y = x. What rule shows the input and output of the reflection, and what is the new coordinate of A'?

Trapezoid ABCD is shown. A is at negative 5, 1. B is at negative 4, 3. C is at negative 2, 3. D is at negative 1, 1.
(x,y)→(y,−x); A' is at (1, 5)
(x,y)→(y,x); A' is at (1, −5) 
(x,y)→(−x,y); A' is at (5, 1) 
(x,y)→(−x,−y); A' is at (5, −1)
This is the complete question and your answer is :
(x,y)→(y,x); A' is at (1, −5) 

Where’s the