What is the output, or dependent variable or
quantity?
X
f(x)
Y

y or f(x), depends on the context.

Step-by-step explanation:

When graphing a function, we input a value, x, and output a value, y. This is why we have a coordinate plane.

For example, if we have y = 2x and x=2, our input, then y = 4, our output.

However, if written in function notation, f(x) = 2x, our output will still be 4, except that our output is f(x)