a.

Since about 95% of a normal distribution falls within two standard deviations of the mean, that leaves 5% that lie without, with 2.5% lying to either side.

b.

About 68% of a normal distribution lies within one standard deviation of the mean, so this probability is about 0.68.
c. You're looking for

such that

Since

occurs for

, it follows that

So there's a probability of 0.10 for having a demand exceeding about 1328 pounds.