It mean Parentheses-exponents-multiplication/division-addition/subtraction and it is the order you do multi step equations
Completing the square follows the principle of taking

and converting it into

where d is the 'correctional number' as I like to call it - i.e. the number that converts the expanded bracket into the +c, since the expanded bracket will give us

.
In this case, 2/2=1 so we have the first part:

.
Expanding this gives us

. We need c to be 9, so we can just add 8.
Putting this together:

Now we can solve it more easily.
Rearranging:
Answer:
The answer for this question is-4
Is the answer 5r-1? I'm not sure tho sorry if it's wrong!