For testing H : = 10 and H : 10, the level of significance, = 0.05 is being considered. What sample

For testing H : μ = 10 and H : μ ≠ 10, the level of significance, α = 0.05 is being considered. What sample size is necessary in order for the probability to be 0.1 of falsely failing to reject H when the true population mean differs from 10 by 0.5? From a preliminary sample, we estimate the value of σ to be 1.25.