What does 15.40 round off to 16 or 15?

What unit of been sure would be appropriate for the volume of a sphere with a radius of 2 meters

Harold wrote this equation to model the level of water in a pool over time. the variable x represents time in hours. f(x) = 3,500 - 225x which statements about the situation are true? check all that apply. the water level is rising. the water level is falling. the initial level of water in the pool was 3,500 units. the initial level of water in the pool was 225 units. the pool was empty after 14 hours. the water was 2,600 units high after 4 hours.

Find the value of x. also give me an explanation so i can complete it to other questions as well, : )