a car cover 100 m in 5th second and 120 m in 8th second during its motion ?calculate the acceleration and distance covered in 20th second?

x(t) = Xo + Vot - 1/2 at^2

So,

(5Vo - 25/2 a)-(4Vo - 16/2 a) = 100
(8Vo - 64/2 a)-(7Vo - 49/2 a) = 120
so,
Vo = 70
a = -20/3

Now just figure x(20)-x(19)