Sets, Relations and Functions: JEE Main 2025 Mathematics question

Let $f: \mathbb{R} \to \mathbb{R}$ be a function defined by $f(x) = (2 + 3a) x^2 + \left( \frac{a + 2}{a - 1} \right) x + b, a \neq 1$. If $f(x + y) = f(x) + f(y) + 1 - \frac{2}{7} xy$, then the value of $28 \sum_{i=1}^{5} |f(i)|$ is