List the intervals on which f is increasing

It really depends,
F = ?
It could be a certain number or choice from a quiz or work.
You must include the choices or your full question, to know how much f is worth.
Mainly if it’s on a graph then it’d be like this.

Using interval notation, it is described as increasing on the interval (1,3). Decreasing: A function is decreasing, if as x increases (reading from left to right), y decreases. In plain English, as you look at the graph, from left to right, the graph goes down-hill. The graph has a negative slope

Source: MathBits