Motivation theorists refer to external rewards people seek to obtain as:

Motivation theorists refer to external rewards people seek to obtain as Incentive.
We call something as incentive, that motivates someone or encourages someone to do something an the theories that suggests that stem of the motivation from the desire to achieve external goals are incentives approaches to motivation.

Find 6% of 3,500 and 4% of 4,000 then subtract the two