A car slows down from 50 m/s to 20 m/s in 6 s. what is the acceleration

Need in all of themmm only answer if you know plsssss

Which of the following is a measure of the amount of light a star directly emits?               a.  luminosity    b.  intensity    c.  wavelength    d.  brightness

What can change the speed of sound as it travels through the ocean? a. salinity only b. density and salinity c. salinity and distance from land d. density and distance from land