What statement describes the meaning of a big$-$O complexity O$($g$($n$))?$

Question $3$Select one:

an estimate of the best$-$case memory usage of a method to solve a problem of size n

an estimate of the average number of runtime operations of a method to solve a problem of size n

an estimate of the best$-$case number of runtime operations of a method to solve a problem of size n

an estimate of the average memory usage of a method to solve a problem of size n

an estimate of the worst$-$case memory usage of a method to solve a problem of size n

an estimate of the worst$-$case number of runtime operations of a method to solve a problem of size n