Milla and luka are 3 kilometers apart and walking toward each other. milla's average speed is 5 kilometers per hour and luka's is 4 kilometers per hour.

Milla's speed is faster and Luka's speed is slower. when the both of them are together, in a line it should look like this:
oThe one with the o is when they would get together again. see that the o is not in the middle. That's what happens when Milla's speed is faster and Luka's speed is slower

Well if you have 20 bats you probably want 20 balls? you don’t have enough context to answer the question.