Truck covers 40 m in 8.5 seconds slowing to a final speed of 2.8 m/s find original speed

V = u + at

2.8 = u + a*8.5

2.8 = u + 8.5a

s = ut + 0.5at^2

40 = u*8.5 + 0.5*a*8.5^2

40 = 8.5u + 36.125a

(2.8 = u + 8.5a) * 8.5

23.8 = 8.5u + 72.25a

Subtract those equations

16.2 = - 36.125a

a = 0.448

2.8 = u + (8.5*-0.448)

2.8 = u - 3.8

u = 6.6 m/s