Answer: 1
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Step-by-step explanation:
We're told that f(x) = -4. That means we can replace the f(x) in the first equation and solve for x.
f(x) = -5x+1
-4 = -5x+1 ..... replaced f(x) with -4
-5x+1 = -4
-5x = -4-1
-5x = -5
x = -5/(-5)
x = 1
As a way to check, we plug in x = 1 to get...
f(x) = -5x+1
f(1) = -5(1)+1
f(1) = -5+1
f(1) = -4
So the answer is confirmed. If f(x) = -4, then x = 1.