given variables list them as independent (x) or as a dependent (y)

I weight of child; prescription dosage

II monthly commision; monthly sales

II ability to concerntrate; level of fatique

IV crop yield; rainfall

An independent variable is the potential stimulus or cause, usually directly manipulated by the experimenter, so it could also be called a manipulative variable.

A dependent variable is the response or measure of results.

Try to figure which factor will effect the other. That will be the independent variable.