
Now completing the square.

(x+5)² = 16 is the rewritten equation... For first question btw.
For the solutions to the equation -

x = -1,-9 is the solution, for the second question.
The answer would be 7/4 because you would just divide both the 21 and 12 by 3
simplify each term
apply the distributive property
-X+3+(-X- -5)
multiple -1 by -5
-X+3+(-x+5)
remove unnecessary parentheses
-x+3-×+5
subtract x from -x
-2x+3+5
add 3 and 5.
-2x+8