Solve the following recurrence relations and express final answer using Big O$-$ notation $($tight bound$)$ show all steps and reasoning that lead to answer a$.$ T$($n$)=\{(1$ if n$=1),($T$($n$-1)+$n if n$>=2)$:$\}$ b$.$ T$($n$)=\{(1$ if n$=1),(4$T$($n$/2)+$nlogn if n$>=2)$:$\}$