you aren't given any probabilistic information on the records themselves, but you do know that the sampling distribution of the sample mean is approximately normal for any reasonably behaved underlying distribution.
the individual cases themselves are distributed with a mean of 8 and standard deviation of 4, so the sample mean is normally distributed with a mean of 8 and a standard deviation of 4/sqrt(90). or,
Xbar ~ N(8, 4/sqrt(90))
now you can find the probability of these events.
i) prob. that the average duration is less than seven years
P(Xbar < 7)
= P(Z < (7-8)/[4/sqrt(90)])
= P(Z < -.4216)
ii) prob. that the average deviation is over 7 years
use a complement rule:
P(Xbar > 7) = 1 - P(Xbar < 7)
iii) prob. that the average deviation is within 1 year
P(7 < Xbar < 9)
and you can split this up as:
= P(Xbar < 9) - P(Xbar < 7)