Question

A proton, moving in negative y-direction in a magnetic field , experiences a force of magnitude F, acting in the negative x direction.
a) What is the direction of the magnetic field producing force?
b) Does your answer change if the word proton is replaced by electron?

I get a little confused when doing the right hand rule but for a) I get Negative z direction and for be it will be the opposite so I get positive z direction. The book says it's the opposite but I don't know how to get that. I point my thumb to the left and then my middle finger to the negative x direction that will be into the page and my index is pointing downwards. So don't know how to get the real answer...