PoS-SoP convertion of function bellow (NOT using K-map)
$$ F=\overline{C} \space \overline{D} +A\overline{D} + A\overline{B}$$

DeMorgan's

$$ \overline F=\overline{\overline{C} \space \overline{D} +A\overline{D} + A\overline{B}}$$

$$ \overline F= (C + D) (\overline A + D) (\overline A + B)$$

First two terms:
$$ \overline F= (C\overline A + D\overline A + CD + DD) (\overline A + B)$$

Simplify:
$$ \overline F= (C\overline A + D) (\overline A + B)$$

Finish multiplying out last term, reduce and take DeMorgan's.

That should get you to your answer.