Which of the following rules represents the set of ordered pairs?
{(1, 2), (2, 3), (4, 5), (7, 8)}
ƒ(x ) = 2x + 1
ƒ(x ) = -x + 4
ƒ(x ) = x + 1

Sub ur points into the answer choices to see which one is true. Keeping in mind that f(x) = y

f(x) = x + 1u will notice that if u sub in ur answer choices into this function, it come out true. 

f(x) = x + 1when x = 1 and y = 2 
2 = 1 + 1
2 = 2 (correct)

f(x) = x + 1...when x = 2 and y = 3
3 = 2 + 1
3 = 3 (correct)

it works for all ur points

so ur answer is : f(x) = x + 1 <==