Please solve the following question with equations and answers. Consider a variable $S$ that follows the process

$dS=dt+dz$

For the first $3$ years, $=6$ and $=5$; for the next $5$ years, $=3$ and $=3.$ If the initial value of the variable is $60,$ the

mean and the variance of the variable at the end of $8$ years are

and

respectively.