Answer
dy/dx=0; i.e. the derivative is 0.
Work Step by Step
y=12 can be rewritten as y=12x$^0$ since x$^0$=1 then using the power rule; dy/dx=0$\times$12x$^{-1}$=0; hence the derivative is 0. You can take this to form a general rule where the derivative of a constant is 0.
