Someone idk how to do this! given the polynomial 21x^4+3y-6x^2+34 1) what polynomial must be subtracted from it to obtain 29x^2-7 ? 2) what polynomial must be added to it to obtain a first degree polynomial?

1) Do 21 X^4 + 3y - 6 X^2 + 34 - (Blah) = 29 X^2 - 7
Since the only terms you have in the solution is X ^ 2 and the constant, you can get rid of 21 X^4 + 3y
Now we have -6 X^2 + 34 - (Blah) = 29 X^2 - 7
-6 X^2 - (-35 X^2) = 29 X^2
34 - (41) = -7
Thus Blah is 21 X^4 + 3y - 35 X^2 + 41

2)First degree polynomials are polynomials where the highest power is 1. Thus you must subtract away 21x^4-6x^2 to get 3y+34

The answer to your question is b