(f o g)(x) = f(g(x))
It means first find the value of g(x), then plug that as the variable into f(x).
g(x) = x-2
That's the only value given for g(x), in other words there's no x to plug into g(x) to spit out a number. So substitute x-2 into f(x).
f(g(x)) = f(x-2) = (2(x-2))/(x-2-3) = (2x-4)/(x-5)
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