Time required : 25.876 s
Further explanation
Given
A car weight = 25000 N
Brake force = 628 N
vo= 6.5 m/s
vt = 0(stop)
Required
time to stop
Solution
W = m . g
25000 = m.10
m=2500 kg
Newton's second law
F = m . a
628 = 2500 . a

vt=vo-at(deceleration a=-)
0=6.5-0.2512.t
0.2512.t=6.5
t=25.876 s