Writing a rule that represents a function using ordered pairs

Question

Each set of ordered pairs represent a function. Write a rule that represents the function. 

(2,10), (4,20), (5,25), (7,35), (9,45)

???

Answer 1

2 x 5 = 10

4 x 5 = 20

5 x 5 = 25

7 x 5 = 35

9 x 5 = 45

 

What rule would this be?