In the first 10s of a body’s motion, the velocity changes from 10 m/s to 20m/s. During the next 30s the velocity changes from 20m/s to 50m/s. What is the average acceleration in m/s^2?

In the first 10s of a body’s motion, the velocity changes from 10 m/s to 20m/s. During the next 30s the velocity changes from 20m/s to 50m/s. What is the average acceleration in m/s^2?
 
(a) 1
 
(b) 2
 
(c) 3
 
(d) 0.5
 
This question was addressed to me during an online interview.
 
I’m obligated to ask this question of Kinematic Equations for Uniformly Accelerated Motion in portion Motion in a Straight Line of Physics – Class 11
Select the correct answer from above options 
Interview Questions and Answers, Database Interview Questions and Answers for Freshers and Experience