Hi,
Re: TY
four shirts, four pants and four pairs of shoes 
Might Recommend you Draw a 'Tree Diagram' to see why the answer is what it is:
FIRST SHIRT
P P P P
S S S S S S S S S S S S S S S S
Each Shirt, makes 16 different outfits:
How many outfits can you make with three shirts, three pants and three pairs of shoes?