polynomials subtraction or addition

Question

not sure what this is and how to do this at all

 

 

-7=-9-k

Answer 1

The object is always to collect like terms.  You can add 9 to both sides, as a beginning.

That gives 9-7 = -k

2 = -k

The objective is to solve for k but 'we' have solved for the opposite.

So you can multiply both sides by -1.

You appear to be in an elementary algebra class.  I hope that your teacher is giving you advice such as what I have done here, and that you learn from these examples. The few techniques need to be understood and mastered, because you have a LOT of algebra ahead of you during your school years.