Data collected by a child development scientist produced a 95% confidence

Data collected by a child development scientist produced a 95% confidence interval for the mean age, μ (in weeks) at which babies began to craw as [21.4, 31.6]

a) what is the sample mean

b) what is the margin of error for the confidence interval

Other factors remaining the same, how would the margin of error for the confidence interval be effected if the confidence level was reduced to 90%?