For this case we have the following functions:
f (x) = 3x + 1
g (x) = x ^ 2 - 6
Subtracting both functions we have:
(f-g) (x) = f (x) - g (x)
(f-g) (x) = (3x + 1) - (x ^ 2 - 6)
(f-g) (x) = 3x + 1 - x ^ 2 + 6
(f-g) (x) = - x ^ 2 + 3x + 7
Answer:
(f-g) (x) = - x ^ 2 + 3x + 7
option B