The distance it will take a car to reach a certain speed, constant acceleration

Question

In 10 seconds car can accelerate to 100km/h. Let's say acceleration is constant, calculate the distance it will take the car to reach 90 km/h after leaving a built-up area where it was moving 60km/h.

$60\frac {km}{h}=16\frac{4}{6}\frac{m}{s}$
$90\frac {km}{h}=25\frac{m}{s}$
I calculated acceleration using $a=\frac {Vp-Vk}{t}=\frac {27\frac{7}{9}-0}{10}=2\frac{7}{9}$
$t=\frac{Vk-Vp}{a}=3$
and distance using $s=\frac {V1+V2}{2}\cdot(t2-t1)=\frac {16\frac{4}{6}+25}{2}\cdot3=[62\frac{1}{2}m]$

I think I got everything right but the result is slightly off, it should be [61,8m] (according to notes)
$s=Vp\cdot t+\frac{a\cdot t^2}{2}$ gives me the same result
What am I doing wrong?