A
(fg) (x) = f(x) * g(x)
(fg) (x) = Sqrt(x) * (5x-8)
Domain is the set of possible x numbers. You can't have a negative inside the square root, so the domain is x greater than or equal to 0.
B
(f/g) (x) = f(x) / g(x)
(f/g) (x) = Sqrt(x) / (5x-8)
x can't be negative (the square root is still there).
The bottom of the fraction can't be 0, so:
5x - 8 = 0
5x = 8
x = 5/8
x can't be 5/8
Domain is x such that x is greater than or equal to 0 and x is not equal to 5/8