5k/6 + 2/3 = 4/5

Wrote in image and in text, pls help

Ms. ortiz sells tomatoes wholesale. the function p(x)=-80x^2+320x-10, graphed below, indicates how much profit she makes on a load of tomatoes if she makes on a load of tomatoes if she sells them for 4-x dollars per kilogram. what should ms. ortiz charge per kilogram of tomatoes to make on a load of tomatoes?

Answer! if you don’t mind, can you explain

At noon a tank contained 10cm water. after several hours it contained 7cm of water. what is the percent decrease of water in the tank?