A made-up greenhouse is kept at a different temperature on each of seven days, and a gardener…

Step 1. $S_{xy}$. With $\bar{x} = 3$, $S_{xy} = \sum (x - 3)y = -27 - 10 - 1 + 0 + 2 + 8 + 24 = -4$.

Step 2. r. $S_{xx} = 9 + 4 + 1 + 0 + 1 + 4 + 9 = 28$ and $S_{yy} = 70.86$. So $r = \dfrac{-4}{\sqrt{28 \times 70.86}} = -0.0898$.

What it means. No. The hours fall and then rise again: a strong U-shaped curve. $r$ is close to $0$ only because $r$ looks for a straight line. Draw the plot and the curve is plain to see.