The acceleration of the skydiver is given by: [tex]a= \frac{v_f-v_i}{t} [/tex] where [tex]v_f=4 m/s[/tex] is the final velocity of the skydiver [tex]v_i=54 m/s[/tex] is the initial velocity of the skydiver [tex]t=0.75 s[/tex] is the time taken for the change of speed
Substituting the numbers into the equation, we find the skydiver's acceleration: [tex]a= \frac{4 m/s-54 m/s}{0.75 s} =-66.7 m/s^2[/tex] where the negative sign means it is a deceleration.