At t=10 ~\text{s}t=10 s, a particle is moving from left to right with a speed of 5.0 ~\text{m/s}5.0 m/s. At t=20 ~\text{s}t=20 s
, the particle is moving right to left with a speed of 8.0 ~\text{m/s}8.0 m/s. Assuming the particle’s acceleration is constant, determine its average acceleration. Assume positive is on the right.