problem-8.12
First check normality, then use t.test() as follows:
> x = babies$dht
> x = x[x<99]
> t.test(x, mu=68, alt="greater")
One Sample t-test
data: x
t = 20.80, df = 743, p-value < 2.2e-16
alternative hypothesis: true mean is greater than 68
...