Hi! I have a question regarding Sets and Functions, please help, thanks!

I have set A{1,2,3,4,5}, B{3,4,5,6,7}, C{5,6,7,8,9}

A union B = {1,2,3,4,,6,7}

A intersection B = {3,4,5}

Define an onto(surjective) function f: A union B -> A intersection B

Define an 1-1 function f: A union B -> A intersection B

2nd part--

Let U = A union B union C

Let D = {x|x,y,z in U) ^ (there exits y)(there exists z)(z = x * y)

U = {1,2,3,4,5,6,7,8,9}

I am not sure how to get set D.

Do I choose a value for y and z from set U and if there is an value for x inside Set U satstify the equation? and if it does, the value for x goes in set D?