Chapter 6, Problem 5PS

Given a normal distribution with $\mu =100$ and $\sigma =10,$ what is the probability that

$\begin{array}{l}\text{a}\text{.}X>75?\\ \text{b}\text{.}X<70?\\ \text{c}\text{.}X<80\text{or}X>110?\\ \text{d}\text{.}\text{Between}\text{what}\text{two}\text{X}\text{Values}\text{(Symmetrically}\text{distributed}\text{around}\text{the}\text{mean)}\text{are}\text{80}\text{percent}\text{of}\text{the}\text{values?}\end{array}$