g•f is the same that g(f(x)) which means that you have to evaluate g(x) with x= f(x), as follows:
g(x) = -x² + 2
g(f(x)) = -(x - 4)² + 2
g(f(x)) = - (x² - 2*x*4 + 4²) + 2
g(f(x)) = - (x² - 8x + 16) + 2
g(f(x)) = -x² + 8x - 16+ 2
g(f(x)) = -x² + 8x - 14
To find (g•f)(-1) you have to replace x = -1 into the expression of g•f, as follows:
(g•f)(-1) = -(-1)² + 8(-1) - 14
(g•f)(-1) = -1 - 8 - 14
(g•f)(-1) = -23
