For my question, $A =\lnot P\land(Q \to R)$. After making the truth table, I managed to get the PDNF of it which is
$$(\lnot p\land q\land r)\lor(\lnot p\land\lnot q\land r)\lor(\lnot p\land\lnot q\land\lnot r).$$
The next part of the question require me to deduce the PDNF of $\lnot A$. Please guide me on how to solve it as most of the other resources I found online are paid-to-use homework websites. Million thanks.