An automobile accelerates from 20 m/s to 50 m/s in 5.0 seconds what is its acceleration

Acceleration is a vector quantity that describes an object's rate of change in velocity.

Given
Vi = 20m/s
Vf = 50m/s
t = 5 s

Hence, a = vf – vi / t. 

Solution: 
A = 50 m/s – 20 m/s / 5s 
A = 6m/s^2

|Acceleration| = (change in speed) / (time for the change)

Change in speed = (50m/s - 20m/s) = 30 m/s
Time for the change = 5.0 sec

|Acceleration| = (30 m/s) / (5 sec)  =  6 m/s² .

I wrote 'Acceleration' with absolute value lines ( |  | ) around it,
because acceleration is actually a vector . . . it should have a
direction as part of its description.  But we don't know anything
about its direction, so we can only talk about its magnitude (size).

Amethod of procedure that has characterized natural science since the 17th century, consisting in systematic observation, measurement, and experiment, and the formulation, testing, and modification of hypotheses.