In this case, $r = 0.066$ and $n = 4$ for quarterly compounding.
APY = $\left(1 + \frac{0.066}{4}\right)^4 - 1$
APY = $\left(1 + 0.0165\right)^4 - 1$
APY = $1.0677 - 1$
APY = $0.0677$
To express this as a percentage, we multiply by 100:
APY = $6.77\%$
So,
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