Lambda calculus expression reduction

Question

I don't know the correct answer how this reduction should've be done. Should I simply put λfx.fx in a place of m and λzy.zzy in a place of n?

(λmnfx.mf(nfx) λfx.fx λzy.zzy)

Answer 1

You have placed parenthesis around the two final variables in the body. I don't see that right-associativity supported in the stated problem where the third abstraction is \zy.zzy not \zy.z(zy).

I believe the answer is \fx.f(ffx) which is equivalent to \fx.f((ff)x).

Also, this is a duplicate question but I'm not sure how to link to the other one.