The solution for given expression is 
 
 
Solution:
Given that rational expression is:

Taking "4" as common term from denominator,
 ------- eqn 1
 ------- eqn 1
Let us use a algebraic identity which is as follows:

So, 
 can be expressed as:
 can be expressed as:

Substitute the above equation in eqn 1,

Cancelling (z + 2y) in numerator and denominator

Thus the solution for given expression is 
