Consider the given monomials. Let us determine the sum of these monomials,
1. 

= 

Therefore, the sum of the given monomials is 
 .
.
2. 

= 

= 

Therefore, the sum of the given monomials is 
 .
.
3. 

= 

Therefore, the sum of the given monomials is 
 .
.
4. 

= 

= 

Therefore, the sum of the given monomials is 
 .
.