You can put this solution on YOUR website! I'm assuming that (fg)(x) means composition of functions, which is usually written as (f o g)(x) or f(g(x)).
This is read as "f-compose-g of x", and means "plug x into g, evaluate, and then plug the result into f".
So if you plug in x into g(x), you get 5x-1.
Now plug that into f(x):
f(x) = 5x + 7
f(5x-1) = 5(5x-1) + 7
f(5x-1) = 25x - 5 + 7
f(5x-1) = 25x + 2
So f(g(x)) = 25x + 2
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