Verified Answer :

(Assuming acceleration is -2.5m/s2) 7.2 seconds.

Muks

a = 2.5 m/s²

since , we have to stop so v = 0 m/s ( final velocity)

u = 18 m/s

t = ?

using ,

⇒ v = u + at

⇒ 0 = 18 + 2.5t

by this we are getting t<0 , since , t cant be -ve , Check your question