How do you balance phosphorus, potassium and nitrogen in water?

Naoki's bicycle has a mass of 10 kg. if naoki sits on her bicycle and starts pedaling with a force of 168 n, causing an acceleration of 2.8 m/s2, what is naoki's mass?

An empty fuel tank can still contain and therefore can be even more dangerous than one full of liquid fuel.

If anyone would be able to me out with these three questions it would be these are from the chem 2202 course.