The answer is deductive reasoning. The deductive reasoning refers to a type of reasoning that starts from the general to go to the particular, deducting or inferring conclusions through certain premises. It is the type of reasoning most used in mathematics.
This is deductive reasoning. You start with the broadest given info that Mary is older than Bill, so any age younger than Bill will be younger than Bill and Mary. So you can draw a conclusion that since Frank is younger than Bill then Mary is older than him as well.
