What is the inverse operation to solve n-9=-18

Ill mark the brainliest if you me with the these three questions 7,8,9

Which expression is equivalent to -12(3x-3/4)

Identify all the cases where non-probability sampling is used when attempting to study the characteristics of a large city. studies on every subject in the population divide a population in groups and obtain a sample studies with a limited amount of time demonstrate existing traits in a population studies with the nth person selected