The train begins to move from a state of rest with an acceleration of a = 0.50m / s, find the time interval t after

The train begins to move from a state of rest with an acceleration of a = 0.50m / s, find the time interval t after which the speed of the train will be equal to v = 72km / h.

Condition:
a = 0.5 m / s ^ 2
V = 72km / h = 20m / s
To find :
t-? sec.
Decision :
V = V0 + at
V = at because V0 = 0.
t = V / a
[t] = m / s / m / s ^ 2 = c ^ 2 / c = c
t = 20 / 0.5 = 40 (sec.)
Answer: 40 sec.