I am not getting the correct answer when i square

Question

You want to obtain a sample to estimate a population mean. Based on previous evidence, you believe the population standard deviation is approximately σ=28.3σ=28.3. You would like to be 95% confident that your estimate is within 4 of the true population mean. How large of a sample size is required? Do not round mid-calculation.

Answer 1

You want the +/- z to be 95% which is +/- 1.96 with z = (x -μ)/(σ/sqrt(n)) = 1.96 (x-mu) = 4

σ/sqrt(n) = 4/1.96 and n = ((1.96/4)28.3)² = 192.29