Acar with a mass of 1245 kg, traveling at +29 m/s strikes another car (2175 kg) traveling at - 10 m/s. if the two cars are entangled together after the collisions, with what velocity will they travel?

Refer to the diagrams shown below.

Consider motion to the right as positive.
Momentum is defined as Mass x Velocity.

Therefore momentum of the system before impact is
P₁ = (1245 kg)*(29 m/s) + (2175 kg)*(-10 m/s) = 14355 (kg-m)/s

After impact, the two cars coalesce and travel together with velocity v.
The momentum after impact is
P₂ = (1245 + 2175 kg)*(v m/s) = 3420v (kg-m)/s

Because momentum is conserved, therefore
3420v = 14355
v = 4.1974 m/s

+ 4.2 m/s