Find ht interval [ z / n + z / n = within which 95 percent of the

Find ht interval [ μ – z σ / √ n μ + z σ / √ n = within which 95 percent of the sample means would be expected to fall, assuming that each sample is from a normal population.
a. μ = 200, σ = 12, n = 36
b. μ = 1,000, σ = 15, n = 9
c. μ = 50, σ = 1, n = 25