PLEASE HELP The position of a particle moving on the x- axis is x= 7.8 + 9.2t -2.1t³ where x is in meters and t is in seconds. What's it's velocity at t= 3.5 seconds and is the velocity constant or continuously changing?​

Consider an ideal gas at 27.0 degrees celsius and 1.00 atmosphere pressure. imagine the molecules to be uniformly spaced, with each molecule at the center of a small cube. what is the length l of an edge of each small cube if adjacent cubes touch but don't overlap?