No sicks,
It's 43/3x + 31/21 = ?
Not 43/x + 31/21 = ?

So it's liek
43/3x + 31/21 = ?
43 + 31 = 21 . 3x
74 = 63x
x = 1.174....

Apologize, I didn't see the 3.

Also, you were wrong.

43/3x + 31/21 = f(x)
f(x) { 43/3x = -31/21 }
f(x) = f(903 = -93x)
x = -9,71....~

And the truth is, the equation can't be solved, but I solved it anyway.

F(x) is a Korea's Girlband.. Fufufu

F(x) =/= f(x)
f(x) is non-variable of x, since there is no real answer for the equation and it only asks for the x, the x has to be defined with just x (or whatever letter you want).
The variable is symbolized by f. There is also g, h, k, etc.

F(x) is also a variable, in this case it means Force.

You guys, thank you for it but here's a better solution.
43/3x + 31/21 = y
x = x

Thanks to algebra I am such a scumbag.

Also do you mind telling me where you get f?

Also F(x) is not a variable nor whatever Sicks is saying.
F = Fluorine (according to the periodic table)
So, F(x) means that you are multiplying the element Fluorine by the variable x.

43/3x + 31/21 =
43/3x=-31/21
-93x=903
x=-9.7096... ≈ -9.7

aren't supposed to be like that?

43/3x + 31/21 = ?
43(21) = -31(3x)
903 = -93x
x = -903/93
x = -9.71

I might have miscalculated some things and I'm lazy to check so yeah.

well close enough
i guess that was the right equation for 8 graders (you're 8 right?)

I'm a 7th grader, my friend.

then that's the most appropriate for you kiddo