(b)
Number of ways of giving one prize for running $= 16$
Number of ways of giving one prizes for swimming $= 16 \times 15$
Number of ways of giving three prizes for riding $= 16 \times 15 \times 14$
$\therefore$ Required ways of giving prizes $= 16 \times 16 \times 15 \times 16 \times 15 \times 14$
$= 16^{3} \times 15^{2} \times 14$