All animals need oxygen. we get oxygen from the air we breathe. how do fish get theirs?

Fish get their oxygen by filtering water through their gills since they don't have lungs like we do.

Distance^2= yellow line ^2 (see picture) = 30^2 + 49^2so distance = squareroot of (300^2 +49^2)i dont know if this is how to solve it, but i cnt think of another way