Arectangle has a perimeter of 84cm and a length 35cm what is its width

I’m stuck on this equation, anyone got the answer?

Gravel is being dumped from a conveyor belt at a rate of 25 ft3/min, and its coarseness is such that it forms a pile in the shape of a cone whose base diameter and height are always equal. how fast is the height of the pile increasing when the pile is 14 ft high? (round your answer to two decimal places.) ft/min

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?