If I am driving down the highway going north at 50 miles per hour, and another car is driving south at 75 miles per hour. How fast is the car coming toward me?

V₂₋₁  = 50 [miles/h]

Explanation:

In order to solve this problem we must use the concept of relative velocities.

Where:

V1 = 50 [miles/h]

V2 = 75 [miles/h]

V₂₋₁ = Relative velocity among the two cars.

V₂₋₁  = 75 - 25 = 50 [miles/h]

That is, the car that goes at 50 miles per hour, sees how the second car approaches at 50 miles per hour.

the answer is b, have negligible mass