If 60 seconds are in a minute, 60 minutes in a hour and 24 hours in a day, than 86,400 seconds are in a day. What type of reasoning g is this?

This is a deductive reasoning.

A deductive reasoning is the use of logic rules to make conclusions from premises considered to be true.

Every statement like 60 seconds are in a minute, and 60 minutes are in a hour, and 24 hours are in a day is a premise.

The conclusion is that there are 86,400 seconds in a day, which comes from:

24 hours / day * 60 minutes / hour * 60 second / minute = 86,400 second / day.