Answer:
He sees the ball coming at him at 150 km/hr
Step-by-step explanation:
Relative velocity is the velocity of Object A as it appears to Observer B moving at a particular velocity. For example when you are in a moving car or vehicle on the road other cars appears to be slower than their original Velocity when they are moving in the same direction.
For the case above the the velocity of the ball to bob(the observer) appears to be faster than its original speed because they're moving in opposite directions.
Vr = Vb + Vo
Vr = relative velocity
Vb = velocity of baseball
Vo = velocity of the observer bob
Vr = 75km/hr + 75km/hr
Vr = 150km/hr
Therefore, bob sees the baseball coming at 150km/hr