I don't understand this equation help !!

An electron moved from shell n = 2 to shell n = 1. what most likely happened during the transition? a fraction of a photon was added. a photon of energy was absorbed. a fraction of a photon was removed. a photon of energy was released.

What is the most common reason for matter changing its state?

There are approximately 15 milliliters (ml) in 1 tablespoon (tbsp). what expression can be used to find the approximate number of milliliters in 3 tbsp?