Length= 9 width= 1
or
length= 8 width= 2
or
length= 7 width= 3
or
length= 6 width= 4
Seven, I think. That's what I found somewhere else.
Step 1
Given;

Required; To find the center that eliminates the linear terms
Step 2



Step 3
Substitute a,d,e into the vertex form


Step 4
Completing the square for -y²+4y



Step 5
Substitute a,d,e into the vertex form

Step 6

Step 7

Hence the answer is (-3,2)