a$)$ Given the following program in which two threads concurrently update one critical resource shared$\_$data without using locks, theoretically, how many different final values may shared$\_$data have? Please explain how each different value is attained by showing the running order of the two functions $($e$.$g$.,$ running order of statements of $8,9,11$ and $16,17,19).($b$)$ Given the following program in which two threads concurrently update one critical resource shared$\_$data, how should you change the program by adding appropriate lock$($s$)$ in order to make the execution result correct $($i$.$e$.,$ same as running the two threads serially$)?$