Answer:
Macbeth hires 2 assassins to kill him
Step-by-step explanation:
He decides to ask this because although Banquo is his best friend Macbeth has become consumed by the thought of power, He will do anything to hold on to it. This contrasts with his original character that would have done anything to please those above him. He is therefore afraid of Banquo as he thinks that he will take his position. This is based on the trust that Macbeth has for the witches at the beginning, they tell him that he will become king and this comes true, they then tell Banquo that his sons will be kings. So afraid of this prophecy he decides to eliminate Banquo. However, the murderers/assassins could not catch Banquo's son and he runs away. So the prophecy still may be true. He also wants Banquo dead as he is suspicious of Macbeth and thinks that he might have killed the king.
This explains why one of the main themes of Macbeth is loyalty, some others are power, prophecy, remorse and supernatural beings.