If (c) were f(k) = -3/k+2, what value of k would be excluded from the domain?

k = - 2 is excluded from the domain

the denominator of f(x) cannot be zero as this would make f(x) undefined. Equating the denominator to zero and solving gives the value that k cannot be

solve k + 2 = 0 ⇒ k = - 2 ← excluded value

not sure but it may be b, as i said i'm not sure.