For $f(x)=8 x-5$ and $g(x)=5 x-8$, find $(f \circ g)(x)$ $(f \circ g)(x)=\square($ Simplify your answer. $)$

Step 1 ：The question is asking for the composition of two functions, \(f(x)\) and \(g(x)\). The composition of two functions, denoted as \((f \circ g)(x)\), is the function \(f(g(x))\). This means that we substitute \(g(x)\) into \(f(x)\). So, we need to substitute \(5x - 8\) into \(f(x)\), which is \(8x - 5\).

Step 2 ：Substitute \(g(x) = 5x - 8\) into \(f(x) = 8x - 5\) to get \(f(g(x)) = 8*(5x - 8) - 5\).

Step 3 ：Simplify \(f(g(x)) = 8*(5x - 8) - 5\) to get \(f(g(x)) = 40x - 69\).

Step 4 ：Final Answer: \((f \circ g)(x) = \boxed{40x - 69}\)