a. (f o g)(x)= f[g(x)] = f(x-5) = (x-5)^2
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b. (g o f)(x)= g[f(x)] = g[x^2] = x^2-5
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c. (f o g)(-3) = f[g(-3)] = f[-8] = 64
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d. (g o f)(-3)= g[f(-3)] = g[9] = 4