This may be a problem where the helpers’ understanding gets in the way of explaining because they do not see why the student is confused. It is just so obvious to the helper.
First, it is traditional that we show a univariate function as y = f(x). (The letters are arbitrary. We could show it as p = h(q), but f, x, and y are traditional.) So y = f(x) is what you are used to. It is called the explicit form of a univariate function.
HOWEVER, it is not always convenient or simple to show a univariate function that way. An alternate way to show it is called the implicit form of a univariate function. That way looks like g(x, y) = some number. That is what we have here. In this case it is easy enough to turn it into the explicit form
[MATH]4x + 3y = 9 \implies 3y = 9 - 4x \implies y = 3 - \dfrac{4x}{3} \implies f(x) = 3 - \dfrac{4x}{3}.[/MATH]
Do you see that the implicit form uses only whole, positive numbers? In that sense, it is simple enough for a second grader to get it. But the explicit form in this case is still quite simple. A third grader can get it.
You are just being asked to work with a function presented a new way.
