Been employed for 2.5 yrs, work is very busy and boss has just recruited someone to assist me. All good, except boss wants me to hand over the majority of my work to new person - all the bits of my job that I like! 
Boss keeps saying it's going to free me up for other stuff (is being a bit vague about what other stuff is) and wants me to supervise the new person's work.
New person is working less hours and getting paid slightly more per annum than me!
I don't want to give up the bits I enjoy most and don't want to supervise anyone either, especially if they're earning more than me.
Saying that, it's not about the money, I'm happy with what I earn. I just feel I don't want to be supervising someone who earns more than me.
I have a good relationship with the boss and they have no complaints about my work, so I am disappointed to have to hand over the bits I like doing.
How would you approach this?