Please help with this, why was the last one wrong?

Consider the pair of functions. f(x) = a}, 900 = x + 7 (a) Find (f0 g)(x). Simplify the results. (1'0 mm = A\" + f -/ Determine the domain of the new function. (Enter your answer using interval notation.) im) -/ (b) Find (9 o f)(x). Simplify the results. (gomxi= w -/ Determine the domain of the new function. (Enter your answer using interval notation.) (0.00) X