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Pearson's r measures the strength and direction of a linear relationship, ranging from −1 to +1. Its square, r², is the fraction of the variance in y explained by the linear fit.
Pearson correlation
r = Σ(x − x̄)(y − ȳ) / √[Σ(x − x̄)²·Σ(y − ȳ)²]
Sxy = 13.5, Sxx = 17.5 and Syy = 13.5, so r = 13.5/√236.25 ≈ 0.8783 — a strong positive relationship explaining about 77% of the variance.
No. A strong r can arise from a common cause, reverse causation or coincidence.