Q$4$: Aggregation$(4$ pt$)$: Given the following relational schema $($attribute types

are omitted for simplicity$)$:

Sailor$($sid$,$ sname, age, rating$)$

Reserve$($sid$,$ bid

Boat$($bid$,$ bname, color$)$

$($a$)$ Find the average age of the sailors $($Hint: Use 'AVG' keyword$)$

$($b$)$ Find the sid of the sailor and the total number of boats reserved by them

$($You should return a table has $($sid$,$ count$))$