Estimation of population standard deviation and standard error of mean?

I'm very confused about how to calculate the population standard deviation and standard error of the mean. Here is the questions:

Oscar T. Grady is the production manager for Citrus Groves Inc., located just north of Ocala, Florida. Oscar is concerned that the last 3 years' late freezes have damaged the 2500 orange trees that Citrus Groves owns. In order to determine the extend of damage to the trees. Oscar has sampled the number of oranges produced per tree for 42 trees and found that the average production was 525 oranges per tree with a standard deviation of 30 oranges per tree.
a) Estimate the population standard deviation from the sample standard deviation.
b) Estimate the standard error of the mean for this finite population.
c) Construct a 98% confidence interval for the mean per-tree output of all 2500 trees.
d) If the mean orange output per tree was 600 oranges 5 years ago, what can Oscar say about the possible existence of damage now?

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