You might like to recall that the pdf of an N(\mu, \sigma^2)
random variable is
f(x) =\frac{1}{\sqrt{2\sigma
^2}}e^{-\frac{(x-\mu)^2}{2\sigma^2}}
and that the probability of a value falling between a and b
is
P(a< x< b) = \int^b_a f(y)dy
Don't forget that the integral is the area under the curve between
two points.
Don't forget that you can look up the cumulative probabilities for
a normal distribution using tables.