We have the following equation:
[tex]28=-k+16-2k-9[/tex]They ask us to solve this equation, in this case, we must solve for "k"
Now, we clear k
[tex]\begin{gathered} 28=-k+16-2k-9 \\ 28=-3k+7 \\ 3k=-28+7 \\ 3k=-21 \\ k=-\frac{21}{3} \\ k=-7 \end{gathered}[/tex]Compared with your solution, this is also correct, let's see the last step in which you are
[tex]\begin{gathered} -3k=21 \\ k=\frac{21}{-3} \\ k=-7 \end{gathered}[/tex]Your solution to this equation is correct in each step you did, you just need to move on to divide the (-3) to the other side
In conclusion, the answer si k = -7
