${n}_{i}=2{\left(\frac{Z\sigma }{E}\right)}^{2}=2{\left(\frac{1.96\text{\hspace{0.17em}}\left(8.1\right)}{3}\right)}^{2}=56.0$

Description:

Math equation. The samples sizes (n) equal 2 times the square of the quantity Z times the pooled estimate of the common standard deviation divided by the margin of error, E. In this case, n= 2 times the square of (1.96 times 8.1) divided by 3. The final answer is 56.0.