Can you please help me with the calculations for the following problem? In particular, is the estimated standard error calculated by the square root of the variance or the square root of the variance/n or the square root/n-1?

A sample is selected from a population with µ = 150. After a treatment is administered to the individuals, the sample mean is found to be M = 145 and the variance equal to 100.

a. If the sample has n = 4 scores, then calculate the estimated standard error and determine whether the sample is sufficient to conclude that the treatment has a significant effect? Use a two-tailed test with α = .05.

b. If the sample has n = 25 scores, then calculate the estimated standard error and determine whether the sample is sufficient to conclude that the treatment has a significant effect? Use a two-tailed test with α = .05.