Question

A body covers 12m in 2nd second and 20m in 4th second. How much distance will it cover in 4 seconds after the 5th second??

Answer 1

With constant acceleration, which I assume you mean, position changes increase linearly in equal time intervals.  This is because constant acceleration means a constant rate of change in velocity.  Velocity is associated with change in position.  From this knowledge we can indicate distances traveled in each of the first nine seconds based on what is known for the 2nd and 4th seconds: