A distance of d is covered with 53 mile/hr initially.
Time taken to cover this distance t1 = d/53 hour
Next distance of d is covered with x mile hours.
Time taken to cover this distance t2 = d/x hours.
We have average speed = 26.5 mile / hour
= Total distance traveled/ total time taken
= 

we know that center of mass is given as
r = (m₁
+ m₂
)/(m₁ + m₂)
taking derivative both side relative to "t"
dr/dt = (m₁ d
/dt + m₂ d
/dt)/(m₁ + m₂)
v = (m₁
+ m₂
)/(m₁ + m₂)
taking derivative again relative to "t" both side
dv/dt = (m₁ d
/dt + m₂ d
/dt)/(m₁ + m₂)
a= (m₁
+ m₂
)/(m₁ + m₂)