Given that ith element of A set cannot be mapped with ith element of B set..So i can range from 1 to 4 i.e one of the 4 values of i..
So we first select that in C(4,1) ways = 4 ways..
Now we are left with 3 elements in A and 5 elements in B..
So for the above constraint i.e. 3 elements in A and 5 elements in B ,
We have no of one one functions = 5P3 = 5! / 2! = 60
So no of one one functions from A to B with A having 4 elements and B having 6 elements
with the given constraint = 4 * 60
= 240
But these are the functions in which ith tuple of A matches with ith tuple of B.
And total no of one one functions possible = 6P4
= 720 / 2 = 360
So no of required functions in which ith tuple does not match = 360 - 240
= 120
Hence 120 should be correct answer..