Use the recursion tree technique to derive the upper bound of the following

recurrences:

a$)$ T$($n$)=$T$($n$/2)+$T$($n$/3)+$T$($n$/6)+$n$,$ while T$(1)=1(15$ points$)$

b$)$ T$($n$)=$T$($n$-1)+$ log n $,$ while T$(1)=1(15$ points$)$