Two Variables · Challenge problem

The points $(1, 2)$, $(2, 2)$, $(3, 4)$, $(4, 4)$ have least-squares line $\hat y = 1 + 0.8x$ and $r^2 = 0.8$. A fifth point is added at $x = 9$, exactly on this line. Find the new $r^2$ to the nearest thousandth.