I am currently studying for an exam and stumbled upon the following task: Given the following problem:

**Input** A set of points $ P \subseteq \mathcal{Q}^2$ and $ k \in \mathbb{N}$

**Question** Find the maximum subset $ S \subseteq P$ such that no three points in $ S$ are collinear.

The task is to find a polynomial time 3-approximation algorithm that is an algorithm that deletes at most $ 3$ -times as many points as an optimal solution. Unfortunately, I am totally clueless here. How would such an algorithm look like?