The equations of motion that relate velocity, distance, time and acceleration for the specific case of "constant acceleration" can be written as follow,
acceleration
a = (v2 - v1)/t
from which v2 = v1 + at
The distance covered during t time d = vav x t, where vav refers to average
velocity in the process from v1 to v2.
For the case of constant acceleration vav = (v1 + v2)/2. Substituting in d we
get d = (v1 + v2)/2 x t
from which,
v2 = 2d/t - v1
If we take the constant acceleration to be zero, a = 0, you can see that the
second equation we wrote becomes,
v2 = v1
(There is no acceleration), so our equation for the distance d becomes,
d = v1 x t = v2 x t