Let $f(x)$ and $g(x)$ be functions. Find $c$ if (f \circ g)(x) = (g \circ f)(x) for all $x$, where $f(x) = 2x + 1$ and $g(x) = -3x + c$.
f(g(x)) = 2(-3x + c) + 1 = -6x + 2c + 1
g(f(x)) = -3(2x + 1) + c = -6x -3 + c
f(g(x)) = g(f(x))
-6x + 2c + 1 = -6x - 3 + c simplify as
c = -4
+1911 
