If f:X→Y and a, b⊆X, then f(a⋂b) is equal to :

Question

I am not getting here that what is a and b are these elements of the set or two subsets of X ?

Comments

I think a and b are two subsets of X, because  $\subseteq$ represents subset here. If it is elements they they should write like a,b $\epsilon$ X.

But even if it is subset then what would be result for following example-

         If X = { 1, 2, 3, 4, 5, 6, ... }

          a= {1, 2, 3, 4} and b= { 3, 4, 5, 6}

And a $\cap$ b = {3, 4 }

So f (3, 4) =  ??