Answer:
A. (0, 4), (4, ∞)
B. (-∞, -4), (4, ∞)
C. (-∞, 0), (0, ∞)
Explanation:
 1
p(x) = -------- ; m(x) = x² - 16
 √x
a.
 p(x)
-------
 m(x) 
 1 1
 -------- --------------
 √x √x
------------------------------ = ---------------------
 x² - 16 (x + 4)(x - 4)
Domain: (0, 4), (4, ∞)
----------------------------------------------------------------------------------------------------------
B.
P(m(x))
 1 1 1
 ------- = ----------------- = ----------------------
 √x √(x² - 16) √(x - 4)(x + 4)
Domain: (-∞, -4), (4, ∞)
----------------------------------------------------------------------------------------------------------------------------
C.
M(p(x))
x² - 16
 1 1
( ------- )² - 16 = ------- - 16
 √x x
Domain: (-∞, 0), (0, ∞)
----------------------------------------------------------------------------------------------------------------------------
I hope this helps!