Answer:
Option b) is the answer
Step-by-step explanation:
A function from X₁ to Y₁ is an object f such that every x in X₁ is uniquely associated with an object f(x) = y in Y₁.
Then
1(b)f={(5,25),(10,5),(15,5),(20,10),(5,25)} is the correct answer.
It follows that
f(5) = 25
f(10) = 5
f(15) = 5
f(20) = 10