The promise of a reward motivates me to accept additional tasks agree or disagree

Agree.

It's a basic human nature to do something that benefit us the most. Whether we realize it or not, Almost everything that we do is motivated by reward. We eat to get the reward of living, we workout to get the reward of health. We work harder if we're promised with greater bonuses. Reward Motivates people. That's is just a simple fact

This is true. Positive reinforcement is more valuable to human beings than is negative reinforcement. With that said, any person who is being promised something rewarding will more likely accept additional tasks than he would, would he not have been promised these tasks. 

You could solve them by trying something new that everyone can agree on or make a decision too.