How can i solve these types of questions for stoichiometry? (explanation )

200. ml of 3.00 m nacl solution is diluted to a final volume of 500. ml. what is the molarity of the final solution?

Ariver current has a velocity of 5km/h relative to the shore, and a boat moves in the same direction as the current at 5 km/h relative to the river. how can the velocity of the boat relative to the shore be calculated?

Pl what kind of reaction is this? nahco3 + h2o → co2 + naoh + h2o -composition -decomposition -single replacement -double replacement im leaning more toward single replacement. if im wrong can you explain whyy?