The sum of polynomials involves adding the polynomials
The other polynomial is 
The sum of the polynomials is given as:

One of the polynomials is given as:

Represent the other polynomial with Q.
So, we have:

Substitute the expressions for P and Sum

Make Q the subject

Evaluate like terms

Hence, the other polynomial is 
Read more about polynomials at:
brainly.com/question/1487158
Answer:
r < 1/3
Step-by-step explanation:
21r<7
Divide each side by 21
21r/21<7/21
r < 1/3
The answer would be C. hope that helps out :)