it would be 4 atm, because the way to figure out the final pressure is that (P1)(V1)=(P2)(V2)
meaning that the original pressure x original volume is equal to the final pressure x final volume. This gas law is called Boyle's law if you'd like to learn more about it.
But (1 atm)(40 mL)=(4 atm)(10 mL)
So it would be the second choice.