A researcher plans to compare two reading instruction methods. From previous research, both groups have a standard deviation of approximately 8 points on the reading assessment. The researcher wants to detect a true difference of 4 points between methods with 80% power at the 0.05 significance level. Using the formula $n = \frac{2(z_{\alpha/2} + z_{\beta})^2 \sigma^2}{d^2}$ where $z_{0.025} ≈ 1.96$ and $z_{0.20} ≈ 0.84$, what is the minimum sample size needed per group?