What is the workdone in bringing two point charges 12microcoulomb and 8microcoulomb,10cm apart,4cm closer

Work, in general, is A = F*s, here A is work, F is force to move a charge in electric field, and s is displacement in the direction of force. If the force is not constant, like in your case, then you have to either use the average value for the force over displacement, or integrate.

Here, the force changes non-linearly with displacement, therefore, integration should be used.

A = Int from s1 to s2: F(s)*ds;
F(s) = (1/(4*pi*eps0))*Q1*Q2*(1/(s^2))

As you can see, the result is irrespective of what charge is moved.