Answer:
x ≥ 3
Explanation:
The domain is the set of x values in a function
The ordered pair ( 3 , 1 ) represents the point where the function starts
( note that the point is "closed" which means that ( 3 , 1 ) represents a solution to the function ) ( which also means that we will be using ≤ or ≥ ) 
The x value of that ordered pair is 3 which means that the domain must include 3. 
The line then goes to the right of the x value 3, infinitely which means that the domain is anything greater than or equal to 3 
or x ≥ 3