a = delta v over delta t delta v is calculated with final velocity less initial velocity so delta v is 0 - 24 that is -24m/s and delta t is calculated with final time less initial time as initial always is 0 then is 15 - 0 that is 15 then a = -24m/s over 15 that is -1,6 then the "acceleration" (on real is a desacceleration) is -1,6m/s^2 (remember that is squared.)
