Use laws of the algebra of sets to show that $X' \cap Y' = (Y \cup X)'$ Use laws of the algebra of sets to show that:

$X' \cap Y' = (Y \cup X)'$

Can I get some help on how to solve this? I have tried so far to use De Morgans Laws to make it go from:

$X' \cap Y'$

to

$(X \cup Y)'$

but how do I switch the letters of x and y around?
so it's like this?

$(Y \cup X)'$ 

I thought at first, to use the commutative laws but that will simply change the union to an intersection which I don't want. 
If I have formatted my question wrong, please tell me so I can know in the future.

Commutativity of sets under set union gives us $$(Y\cup X)' = (X\cup Y)'$$
Furthermore, it is also true that sets commute under set intersection: $A\cap B = B\cap A$.
