Function:
A function is a relation in which each input (x) has only one output (y).
If any one input (x) has more than one output (y) then it is not a function.
As you can see from the given table, the value of (a) must be anything other than (2)
So we can set a value of 4 for (a)
Now if you notice, each input will have exactly one output value so the criteria of a function is satisfied.
So, the answer is 4
