Deceleration formula

Deceleration is a type of acceleration (with a negative value). So, you just use the acceleration formula).

Find the acceleration with
A = (Vfinal - Vinitial) / T
(Vfinal is 0 so the result will be negative).

Then plug the value for A into the normal formula

D = Vinitial * T + 1/2 * A * T ^ 2

Or you could say the average speed is three and a half meters per second and multiply the average speed times the time.

Assuming the deceleration is constant. Then
a(t)=A (A<0)
v(t)=7+At
v(1.71)=7+1.71A
A=-1.71/7
s(t)=7t-1.71/14 t^2
s(1.71)=7(1.71) - (1.71)^3/14=11.613 m (3dp)

Thanks guys. I haven't had the chance to check the maths against the what I'm seeing at the machine yet. It'll be next week now.