Answer:
V²=U² + 2as
Where V=Final Velocity
U=Initial Velocity
a=acceleration ( Deceleration in this case)
s=distance covered
10² = 30² + 2(a)(20)
100 = 900 + 40a
100 - 900 = 40a
-800=40a
a= -800/40
a= -20ms-².
Its negative because the car Decelerated.
