The velocity of the speeder is expressed by the equation:
v1 = d1 / t1 --> d1 = v1 t1
And for the police:
d2= v2i t2 + 0.5 a2 t2^2
where v is final velocity, vi is initial velocity, d is distance, a is acceleration and t is time
The distance of the two must be equal when the police overtakes the speeder hence:
v1 t1 = v2i t2 + 0.5 a2 t2^2
t1 = t2 = t and v2i = 0 since the police starts at rest, so:
26.8 t = 0.5 * 2.4 * t^2
26.8 = 1.2 t
t = 22.33 seconds